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/compassMapPlugin.dart

@@ -1,6 +1,5 @@
 import 'dart:async';
 
-import 'package:comunes_flutter/comunes_flutter.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_map/flutter_map.dart';
 
@@ -78,7 +77,8 @@ class _CompassMapPluginWidgetState extends State<CompassMapPluginWidget> {
                   Positioned(
                     top: 10.0,
                     right: 10.0,
-                    child: CenteredRow(
+                    child: Row(
+                      mainAxisAlignment: MainAxisAlignment.center,
                       children: <Widget>[
                         Column(
                           children: <Widget>[