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/models/fireNotificationsPersist.dart

@@ -1,7 +1,6 @@
 import 'dart:async';
 import 'dart:convert';
 
-import 'package:comunes_flutter/comunes_flutter.dart';
 import 'package:shared_preferences/src/shared_preferences_legacy.dart';
 
 import '../globals.dart' as globals;
@@ -11,7 +10,8 @@ const String fireNotificationKey = 'fireNotifications';
 
 Future<List<FireNotification>> loadFireNotifications() async {
   return globals.prefs.then((SharedPreferences prefs) {
-    final List<String>? FireNotifications = prefs.getStringList(fireNotificationKey);
+    final List<String>? FireNotifications =
+        prefs.getStringList(fireNotificationKey);
     final List<FireNotification> persistedList = <FireNotification>[];
     for (final String notificationString in (FireNotifications ?? <String>[])) {
       final Map<String, dynamic> notificationMap =
@@ -26,7 +26,9 @@ void persistFireNotifications(List<FireNotification> notif) {
   // print('Persisting $notif');
   globals.prefs.then((SharedPreferences prefs) {
     final List<String> notifAsString = <String>[];
-    notif.where(notNull).toList().forEach((FireNotification notification) {
+    notif
+        .whereType<FireNotification>()
+        .forEach((FireNotification notification) {
       notifAsString.add(json.encode(notification.toJson()));
     });
     prefs.setStringList(fireNotificationKey, notifAsString);