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/activeFires.dart

@@ -1,6 +1,5 @@
 import 'dart:async';
 
-import 'package:comunes_flutter/comunes_flutter.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_redux/flutter_redux.dart';
 import 'package:flutter_speed_dial/flutter_speed_dial.dart';
@@ -17,6 +16,7 @@ import 'models/appState.dart';
 import 'models/yourLocation.dart';
 import 'placesAutocompleteUtils.dart';
 import 'redux/actions.dart';
+import 'widgets/rounded_btn.dart';
 
 @immutable
 class _ViewModel {
@@ -264,19 +264,21 @@ class _ActiveFiresPageState extends State<ActiveFiresPage> {
                           return completer.future;
                         })
                     : Center(
-                        child: CenteredColumn(children: <Widget>[
-                        RoundedBtn(
-                            icon: Icons.location_searching,
-                            text: S.of(context).addYourCurrentPosition,
-                            onPressed: () => onAddYourLocation(view.onAdd),
-                            backColor: fires600),
-                        const SizedBox(height: 26.0),
-                        RoundedBtn(
-                            icon: Icons.edit_location,
-                            text: S.of(context).addSomePlace,
-                            onPressed: () => onAddOtherLocation(view.onAdd),
-                            backColor: fires600),
-                      ])),
+                        child: Column(
+                            mainAxisAlignment: MainAxisAlignment.center,
+                            children: <Widget>[
+                            RoundedBtn(
+                                icon: Icons.location_searching,
+                                text: S.of(context).addYourCurrentPosition,
+                                onPressed: () => onAddYourLocation(view.onAdd),
+                                backColor: fires600),
+                            const SizedBox(height: 26.0),
+                            RoundedBtn(
+                                icon: Icons.edit_location,
+                                text: S.of(context).addSomePlace,
+                                onPressed: () => onAddOtherLocation(view.onAdd),
+                                backColor: fires600),
+                          ])),
           );
         });
   }