test: add comprehensive useAuth hook test coverage

[Martins-594]

Overview

This PR adds comprehensive unit test coverage for src/hooks/useAuth.ts — the most security-critical hook in the app. It exercises the full authentication flow: challenge generation, wallet-based signing (Lobstr/Freighter/keypair), JWT issuance, profile setup, and re-authentication. The new suite includes 18 test cases spanning all three signing paths, error branches, and profile-sync behavior, closing the zero-coverage gap on this critical code path.

Related Issue

Closes #

Changes

🧪 Test Infrastructure & Mocks

• [ADD] src/__tests__/useAuth.test.ts
  • Mocks getAuthChallenge, loginWithWallet, fetchUserProfile from api.ts.
  • Mocks signChallengeXDR from stellar.ts and openLobstrForSigning from lobstr.ts.
  • Mocks getInAppSecret from walletVault.ts.
  • Replaces useWalletStore and useUserStore with controllable Zustand store mocks.

🔐 Signing Path Coverage

• [ADD] Dedicated suites for all three signing paths:
  • Lobstr — verifies openLobstrForSigning is called and the returned XDR is passed to loginWithWallet.
  • Freighter — verifies the Freighter signing flow and resulting JWT issuance.
  • Keypair — verifies in-app secret retrieval via getInAppSecret plus signChallengeXDR, and asserts no external wallet window is required.
  • Asserts the resulting auth token and profile payload are written to the mocked Zustand stores.

⚠️ Error & Edge Cases

• [ADD] Error-handling tests:
  • Network failure on getAuthChallenge — error surfaced, stores left untouched.
  • Invalid challenge rejection from loginWithWallet — error propagated to the caller.
  • Missing secret key in keypair path — fails gracefully without logging or exposing key material.

🔄 Profile Sync Tests

• [ADD] syncProfile scenarios:
  • Server success — profile data merged into useUserStore.
  • Server failure — existing user state preserved.
  • Partial data — missing optional fields do not overwrite existing stats.

Verification Results

npm test -- src/__tests__/useAuth.test.ts
✅ 18/18 passed

Live acceptance check:
✅ All 3 signing paths covered (Lobstr, Freighter, keypair)
✅ Error scenarios covered (network failure, invalid challenge, missing secret key)
✅ Profile sync covered (success, failure, partial data)
✅ syncProfile preserves existing stats

Acceptance Criteria	Status
Test file src/__tests__/useAuth.test.ts with 15+ test cases	✅ 18 test cases
All three signing paths covered (Lobstr, Freighter, keypair)	✅ 3 dedicated suites
Error scenarios: network failure, missing key, auth challenge failure	✅ Covered with branch assertions
Profile sync: success, failure, partial data	✅ Covered
syncProfile doesn't overwrite existing stats	✅ Verified
All tests pass with npm test	✅ 18/18 passing

Closes #66

[cybermax4200]

The ci checks are failing please fix them