feat(flutter): project scaffold with pubspec and smoke test

iOS + Android targets only; desktop disabled (per spec, Tauri-wrapped
SvelteKit handles desktop in v1.1). Riverpod + dio + just_audio +
audio_service + go_router pinned in pubspec. Smoke test confirms the
ProviderScope wiring boots a Material app.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/pubspec.yaml

@@ -0,0 +1,39 @@
+name: minstrel
+description: Minstrel mobile client
+publish_to: 'none'
+version: 0.1.0+1
+
+environment:
+  sdk: '>=3.5.0 <4.0.0'
+  flutter: '>=3.24.0'
+
+dependencies:
+  flutter:
+    sdk: flutter
+  flutter_riverpod: ^2.5.1
+  dio: ^5.7.0
+  just_audio: ^0.9.40
+  audio_service: ^0.18.15
+  flutter_secure_storage: ^9.2.2
+  go_router: ^14.6.1
+  flutter_svg: ^2.0.16
+  google_fonts: ^6.2.1
+  package_info_plus: ^8.0.0
+  pub_semver: ^2.1.4
+  cupertino_icons: ^1.0.8
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^4.0.0
+  mocktail: ^1.0.4
+
+flutter:
+  uses-material-design: true
+  # assets:
+  #   - assets/svg/
+  #   - assets/error-copy.json
+  #   - shared/fabledsword.tokens.json
+  # NOTE: Task 5 will sync assets/ + shared/ and uncomment the block above.
+  # The flutter test runner refuses to build a bundle with missing asset
+  # paths, even though `flutter pub get` and `flutter analyze` only warn.