refactor: improve biometric authentication and unify sign-in state

- Refactor `BiometricInteractor` on Android to use `Application.ActivityLifecycleCallbacks` for automatic activity tracking, eliminating the manual `BiometricActivityHolder`.
- Consolidate `SignInViewModel` UI state into a single `SignInResult` data class, replacing separate flows for result and visibility with atomic state updates.
- Update `SignInScreen` and related tests to utilize the unified state model.
- Downgrade `androidx.biometric` to `1.1.0` for stability and set `minSdk` to 23 in `CONTRIBUTING.md`.
- Add `USE_FINGERPRINT` permission to `AndroidManifest.xml` and remove manual `configChanges` handling for `MainActivity`.
- Expand `CONTRIBUTING.md` with detailed coding standards for named arguments, state management, and Composable patterns.
- Switch iOS project configuration to use automatic code signing.
- Ensure `BiometricInteractor` operations are explicitly dispatched to the main thread when interacting with UI components.

Author: softartdev

CONTRIBUTING.md

@@ -27,7 +27,7 @@ NoteDelight is a **Kotlin Multiplatform** note-taking application with database
 
 ### Supported Platforms
 
-- ✅ Android (minSdk 24)
+- ✅ Android (minSdk 23)
 - ✅ iOS (14.0+)
 - ✅ Desktop (Windows, macOS, Linux)
 - ✅ Web (WebAssembly, experimental)
@@ -89,6 +89,60 @@ kotlin.code.style=official
 - One blank line between functions
 - Two blank lines between top-level declarations
 - No blank lines at start/end of blocks
+- Inside an `expect`/`interface` body with several method signatures, separate them with blank lines so the
+  declaration list reads as members rather than a wall of text:
+  ```kotlin
+  expect class BiometricInteractor {
+
+      suspend fun canAuthenticate(): Boolean
+
+      fun hasStoredPassword(): Boolean
+      // ...
+  }
+  ```
+
+#### Call Sites & Lambdas
+- **Use named arguments** when calling a function with three or more parameters, or whenever the call site
+  would otherwise need a same-typed positional argument list. This is especially important for
+  cross-platform interactors and view-model actions:
+  ```kotlin
+  biometricInteractor.encryptAndStorePassword(
+      password = password,
+      title = title,
+      subtitle = subtitle,
+      negativeButton = negativeButton,
+  )
+  ```
+- **Annotate non-trivial local types** so the reader does not have to follow inference through several
+  generics or platform calls (`val res: DecryptedPasswordResult = ...`, `val plain: ByteArray = ...`).
+- **Order `when` branches by the success path first**, error/`else` branches afterwards — this matches the
+  way ViewModels read top-to-bottom in the project. Prefer `when (result) { is Success -> ...; else -> ... }`
+  over an inverted `if (!success) ... else ...` ladder.
+- **Collapse trivial `viewModelScope.launch` blocks to a single line** when their body is one statement
+  (e.g. `private fun cancel() = viewModelScope.launch { router.popBackStack() }`).
+- **Compose state edits**: prefer a single `mutableStateFlow.update { it.copy(...) }` that sets every field
+  affected by an event over multiple chained `update` calls. It keeps the resulting state atomic and
+  makes the visible transition obvious.
+
+#### Composables, strings, and event arguments
+- **Do not pipe localized strings through actions or screen wrappers as empty placeholders.** If a screen
+  needs a `stringResource` to dispatch an action, read it directly at the call site:
+  ```kotlin
+  // ❌ Avoid
+  onClick = { onAction(SignInAction.OnBiometricClick("", "", "")) }
+  // ...wrapper that overwrites the empty strings before forwarding to the ViewModel.
+
+  // ✅ Prefer
+  val title = stringResource(Res.string.biometric_prompt_title)
+  val subtitle = stringResource(Res.string.biometric_prompt_subtitle)
+  val negative = stringResource(Res.string.biometric_prompt_negative_button)
+  onClick = { onAction(SignInAction.OnBiometricClick(title, subtitle, negative)) }
+  ```
+  When the strings are needed inside a stateless `…Body` composable that also has its own preview, expose
+  them as defaulted parameters (`title: String = stringResource(Res.string.…)`) instead of forwarding the
+  action with empty strings and then re-resolving them in the stateful wrapper.
+- **Prefer method references for forwarding callbacks** (`onAction = signInViewModel::onAction`) when the
+  wrapper performs no transformation.
 
 ### Code Organization
 

app/android/src/main/AndroidManifest.xml

@@ -2,6 +2,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
     <uses-permission android:name="android.permission.USE_BIOMETRIC" />
+    <uses-permission android:name="android.permission.USE_FINGERPRINT" android:maxSdkVersion="28" />
 
     <application
         android:name=".MainApplication"
@@ -11,7 +12,6 @@
         android:theme="@style/Theme.NoteDelight">
         <activity
             android:name=".MainActivity"
-            android:configChanges="orientation|screenSize|keyboardHidden"
             android:exported="true"
             android:windowSoftInputMode="adjustResize">
             <intent-filter>

app/android/src/main/java/com/softartdev/notedelight/MainActivity.kt

@@ -3,23 +3,13 @@ package com.softartdev.notedelight
 import android.os.Bundle
 import androidx.activity.compose.setContent
 import androidx.appcompat.app.AppCompatActivity
-import com.softartdev.notedelight.interactor.BiometricActivityHolder
-import org.koin.android.ext.android.inject
 
 class MainActivity : AppCompatActivity() {
 
-    private val biometricActivityHolder: BiometricActivityHolder by inject()
-
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        biometricActivityHolder.attach(this)
         setContent {
             App()
         }
     }
-
-    override fun onDestroy() {
-        biometricActivityHolder.detach()
-        super.onDestroy()
-    }
 }

app/iosApp/iosApp.xcodeproj/project.pbxproj

@@ -460,12 +460,10 @@
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				CLANG_ENABLE_MODULES = YES;
 				CODE_SIGN_IDENTITY = "Apple Development";
-				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "iPhone Developer";
-				CODE_SIGN_STYLE = Manual;
+				CODE_SIGN_STYLE = Automatic;
 				CURRENT_PROJECT_VERSION = 19;
 				DEVELOPMENT_ASSET_PATHS = "\"iosApp/Preview Content\"";
-				DEVELOPMENT_TEAM = "";
-				"DEVELOPMENT_TEAM[sdk=iphoneos*]" = H7L7R3VNZ4;
+				DEVELOPMENT_TEAM = H7L7R3VNZ4;
 				ENABLE_PREVIEWS = YES;
 				GENERATE_INFOPLIST_FILE = NO;
 				INFOPLIST_FILE = iosApp/Info.plist;
@@ -475,7 +473,7 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-            				MARKETING_VERSION = 8.5.4;
+				MARKETING_VERSION = 8.5.4;
 				OTHER_LDFLAGS = (
 					"$(inherited)",
 					"-ObjC",
@@ -487,7 +485,6 @@
 				PRODUCT_BUNDLE_IDENTIFIER = com.softartdev.notedelight;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
-				"PROVISIONING_PROFILE_SPECIFIER[sdk=iphoneos*]" = NoteDelight_Development_Profile;
 				SWIFT_OBJC_BRIDGING_HEADER = "iosApp-Bridging-Header.h";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
@@ -517,7 +514,7 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-            				MARKETING_VERSION = 8.5.4;
+				MARKETING_VERSION = 8.5.4;
 				OTHER_LDFLAGS = (
 					"$(inherited)",
 					"-ObjC",

app/iosApp/iosApp.xcworkspace/xcuserdata/artur.xcuserdatad/UserInterfaceState.xcuserstate

@@ -22,8 +22,10 @@ import com.softartdev.notedelight.usecase.settings.ExportDatabaseUseCase
 import com.softartdev.notedelight.usecase.settings.ImportDatabaseUseCase
 import com.softartdev.notedelight.usecase.settings.RevealFileListUseCase
 import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.test.runTest
 import org.junit.After
+import org.junit.Before
 import org.junit.Rule
 import org.junit.Test
 import org.mockito.Mockito
@@ -64,6 +66,16 @@ class SettingsViewModelTest {
         coroutineDispatchers = coroutineDispatchers,
     )
 
+    @Before
+    fun stubBiometricDefaults() {
+        // Mockito returns null for unstubbed suspend methods; unboxing the null Boolean inside
+        // updateSwitches() would NPE and route to ErrorDialog, breaking unrelated tests.
+        runBlocking {
+            Mockito.`when`(mockBiometricInteractor.canAuthenticate()).thenReturn(false)
+        }
+        Mockito.`when`(mockBiometricInteractor.hasStoredPassword()).thenReturn(false)
+    }
+
     @After
     fun tearDown() = runTest {
         Mockito.reset(mockSafeRepo, mockSnackbarInteractor, mockRouter, mockAppVersionUseCase, mockBiometricInteractor)

core/presentation/src/androidHostTest/kotlin/com/softartdev/notedelight/presentation/settings/SettingsViewModelTest.kt

@@ -49,15 +49,15 @@ class SignInViewModelTest {
     @Test
     fun showSignInForm() = runTest {
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
             cancelAndIgnoreRemainingEvents()
         }
     }
 
     @Test
     fun onSettingsClick() = runTest {
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
 
             signInViewModel.onAction(SignInAction.OnSettingsClick)
             Mockito.verify(mockRouter).navigateClearingBackStack(route = AppNavGraph.Settings)
@@ -69,7 +69,7 @@ class SignInViewModelTest {
     @Test
     fun navMain() = runTest {
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
 
             val pass = StubEditable("pass")
             Mockito.`when`(mockCheckPasswordUseCase(pass)).thenReturn(true)
@@ -84,10 +84,10 @@ class SignInViewModelTest {
     @Test
     fun showEmptyPassError() = runTest {
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
 
             signInViewModel.onAction(SignInAction.OnSignInClick(pass = StubEditable("")))
-            assertEquals(SignInResult.ShowEmptyPassError, awaitItem())
+            assertEquals(SignInResult.State.ShowEmptyPassError, awaitItem().state)
 
             cancelAndIgnoreRemainingEvents()
         }
@@ -96,12 +96,12 @@ class SignInViewModelTest {
     @Test
     fun showIncorrectPassError() = runTest {
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
 
             val pass = StubEditable("pass")
             Mockito.`when`(mockCheckPasswordUseCase(pass)).thenReturn(false)
             signInViewModel.onAction(SignInAction.OnSignInClick(pass))
-            assertEquals(SignInResult.ShowIncorrectPassError, awaitItem())
+            assertEquals(SignInResult.State.ShowIncorrectPassError, awaitItem().state)
 
             cancelAndIgnoreRemainingEvents()
         }
@@ -110,7 +110,7 @@ class SignInViewModelTest {
     @Test
     fun showError() = runTest {
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
 
             val throwable = Throwable()
             Mockito.`when`(mockCheckPasswordUseCase(anyObject())).thenThrow(throwable)
@@ -127,10 +127,10 @@ class SignInViewModelTest {
     fun refreshBiometricVisibleWhenAvailable() = runTest {
         Mockito.`when`(mockBiometricInteractor.hasStoredPassword()).thenReturn(true)
         Mockito.`when`(mockBiometricInteractor.canAuthenticate()).thenReturn(true)
-        signInViewModel.biometricVisibleFlow.test {
-            assertFalse(awaitItem())
+        signInViewModel.stateFlow.test {
+            assertFalse(awaitItem().biometricVisible)
             signInViewModel.onAction(SignInAction.RefreshBiometric)
-            assertTrue(awaitItem())
+            assertTrue(awaitItem().biometricVisible)
             cancelAndIgnoreRemainingEvents()
         }
     }
@@ -142,7 +142,7 @@ class SignInViewModelTest {
             .thenReturn(DecryptedPasswordResult.Success(pass))
         Mockito.`when`(mockCheckPasswordUseCase(pass)).thenReturn(true)
         signInViewModel.stateFlow.test {
-            assertEquals(SignInResult.ShowSignInForm, awaitItem())
+            assertEquals(SignInResult(), awaitItem())
             signInViewModel.onAction(SignInAction.OnBiometricClick("t", "s", "c"))
             Mockito.verify(mockRouter).navigateClearingBackStack(route = AppNavGraph.Main)
             cancelAndIgnoreRemainingEvents()
@@ -153,11 +153,11 @@ class SignInViewModelTest {
     fun biometricSignInUnavailableClearsState() = runTest {
         Mockito.`when`(mockBiometricInteractor.decryptStoredPassword(anyObject(), anyObject(), anyObject()))
             .thenReturn(DecryptedPasswordResult.Failure(BiometricResult.Unavailable))
-        signInViewModel.biometricVisibleFlow.test {
-            assertFalse(awaitItem())
+        signInViewModel.stateFlow.test {
+            assertFalse(awaitItem().biometricVisible)
             signInViewModel.onAction(SignInAction.OnBiometricClick("t", "s", "c"))
             Mockito.verify(mockBiometricInteractor).clearStoredPassword()
             cancelAndIgnoreRemainingEvents()
         }
     }
-}
+}