feat(activities): add autocomplete & what's new popup

Features:
- Add autocomplete support for Activity search with Google Places API.
- Add "What's New" popup system to showcase new features on app update.
- Implement logic to detect fresh installs vs updates.

Fixes:
- Switch API key handling to use Firebase config for Release mode support.
- Refactor map pins to be consistent (red pins).
- UI fixes on Create Trip page (overflow issues).

Refactor:
- Make WhatsNewDialog reusable by accepting features list as parameter.

lib/pages/home.dart

@@ -14,6 +14,8 @@ import '../blocs/auth/auth_event.dart';
 import '../services/error_service.dart';
 import '../services/notification_service.dart';
 import '../services/map_navigation_service.dart';
+import '../services/whats_new_service.dart';
+import '../components/whats_new_dialog.dart';
 
 class HomePage extends StatefulWidget {
   const HomePage({super.key});
@@ -57,6 +59,45 @@ class _HomePageState extends State<HomePage> {
         });
       }
     });
+
+    // Vérifier les nouveautés
+    WidgetsBinding.instance.addPostFrameCallback((_) async {
+      await _checkAndShowWhatsNew();
+    });
+  }
+
+  Future<void> _checkAndShowWhatsNew() async {
+    final service = WhatsNewService();
+    if (await service.shouldShowWhatsNew()) {
+      if (!mounted) return;
+      showDialog(
+        context: context,
+        barrierDismissible: false,
+        builder: (context) => WhatsNewDialog(
+          onDismiss: () => Navigator.pop(context),
+          features: const [
+            WhatsNewItem(
+              icon: Icons.map_outlined,
+              title: 'Recherche globale',
+              description:
+                  'Recherchez des restaurants, musées et plus encore directement depuis la carte.',
+            ),
+            WhatsNewItem(
+              icon: Icons.search,
+              title: 'Autocomplétion améliorée',
+              description:
+                  'Découvrez des suggestions intelligentes lors de la recherche de lieux et d\'activités.',
+            ),
+            WhatsNewItem(
+              icon: Icons.warning_amber_rounded,
+              title: 'Alertes de distance',
+              description:
+                  'Soyez averti si une activité est trop éloignée de votre lieu de séjour.',
+            ),
+          ],
+        ),
+      );
+    }
   }
 
   Widget _buildPage(int index) {