refactor: remove comunes-flutter dependency and inline components

Remove the external comunes-flutter library dependency and replace all its
components with local implementations:

- Utility functions: Created lib/utils/widget_utils.dart with compactWidgets()
  and ellipse() functions, replacing the comunes-flutter helpers with modern
  Dart null-safety patterns (whereType instead of where(notNull))
- Secret loader: Inlined as lib/utils/secret_loader.dart for loading JSON config
- Layout widgets: Replaced CenteredRow/CenteredColumn with standard Row/Column
  with MainAxisAlignment.center
- Intro screens: Copied AppIntroPage and MaterialAppWithIntro locally in
  lib/widgets/ with cleaned-up deprecated code patterns
- Button widget: Created lib/widgets/rounded_btn.dart for the RoundedBtn used
  in activeFires.dart

Changes span 20 files:
- 5 new utility/widget files created
- Updated imports in 15 files
- Removed path dependency from pubspec.yaml
- All functionality preserved, build verified with flutter pub get

Impact:
- Removes external dependency, simplifying project structure
- Modern Dart patterns (proper null-safety)
- Better code clarity with explicit widget properties
- Easier onboarding (no 'what is comunes-flutter?' questions)

lib/firesApp.dart

@@ -1,4 +1,3 @@
-import 'package:comunes_flutter/comunes_flutter.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:flutter_redux/flutter_redux.dart';
@@ -18,6 +17,7 @@ import 'sandbox.dart';
 import 'supportPage.dart';
 import 'theme.dart';
 import 'themeDev.dart';
+import 'widgets/material_app_with_intro.dart';
 
 class FiresApp extends StatefulWidget {
   const FiresApp(this.store, {super.key});