Adds firebase_core + firebase_analytics and a FirebaseAnalyticsBackend that
adapts the existing AnalyticsBackend interface to GA4. Kept in its own file
so the typed AnalyticsService and DebugAnalyticsBackend stay free of the
firebase dependency (unit tests never pull in platform channels).
Not yet wired into main() — that needs lib/firebase_options.dart from
flutterfire configure (owner step). All 161 tests still green.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
SaveRepository (versioned JSON over prefs) with best-result merging and
unlock walking; ContentRepository loads the bundled pack; SeasonFlow/
Progress notifiers orchestrate stage start -> win record -> advance.
Season map grid with stars/locks, Home -> Map -> Game navigation,
close button, next-stage action on the win overlay.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Pure-Dart WAV synthesizer (tool/gen_sfx.dart) generates place/clear/
combo/win/lose effects; AudioService player pool fires on placement,
line clears, combo streaks, and phase transitions.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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