Fix dark mode across Astroshots

[calvin-archastro]

Summary

• make the shared Astroshots palette adapt to macOS Aqua and Dark Aqua
• replace fixed white cards across Settings, stream, detail, friction-log, overlay, and review-sheet surfaces with semantic elevated surfaces
• explicitly inherit the matching foreground color throughout tray content
• preserve intentionally black fullscreen review chrome
• add contrast regression tests for both macOS appearances

Root cause

The app mixed fixed light backgrounds with unstyled SwiftUI text. When macOS switched to dark mode, system text became light while cards remained white, making labels disappear. Backgrounds and foregrounds now switch together through the shared theme.

Verification

• xcodebuild -project macos/Astroshots.xcodeproj -scheme Astroshots -configuration Debug -derivedDataPath macos/build/DerivedData-dark-mode -skipPackagePluginValidation -only-testing:AstroshotsTests test CODE_SIGNING_ALLOWED=NO — 60 tests passed
• npm run test:changelog — 2 tests passed
• git diff --check