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/services/activity_places_service.dart

@@ -654,4 +654,72 @@ class ActivityPlacesService {
       throw Exception('Erreur HTTP ${response.statusCode}');
     }
   }
+
+  /// Récupère des suggestions d'autocomplétion
+  Future<List<Map<String, String>>> fetchSuggestions({
+    required String query,
+    double? lat,
+    double? lng,
+  }) async {
+    if (query.isEmpty) return [];
+
+    try {
+      String url =
+          'https://maps.googleapis.com/maps/api/place/autocomplete/json'
+          '?input=${Uri.encodeComponent(query)}'
+          '&key=$_apiKey'
+          '&language=fr';
+
+      if (lat != null && lng != null) {
+        url += '&location=$lat,$lng&radius=50000'; // 50km bias
+      }
+
+      final response = await http.get(Uri.parse(url));
+
+      if (response.statusCode == 200) {
+        final data = json.decode(response.body);
+        if (data['status'] == 'OK') {
+          return (data['predictions'] as List).map<Map<String, String>>((p) {
+            return {
+              'description': p['description'] as String,
+              'placeId': p['place_id'] as String,
+            };
+          }).toList();
+        }
+      }
+      return [];
+    } catch (e) {
+      LoggerService.error('ActivityPlacesService: Erreur autocomplete: $e');
+      return [];
+    }
+  }
+
+  /// Récupère une activité via son Place ID
+  Future<Activity?> getActivityByPlaceId({
+    required String placeId,
+    required String tripId,
+  }) async {
+    try {
+      final details = await _getPlaceDetails(placeId);
+      if (details == null) return null;
+
+      // Créer une map simulant la structure "place" attendue par _convertPlaceToActivity
+      // Note: _getPlaceDetails retourne "result", qui est déjà ce qu'on veut,
+      // mais _convertPlaceToActivity attend le format "search result" qui a geometry au premier niveau.
+      // Heureusement _getPlaceDetails retourne une structure compatible pour geometry/photos etc.
+
+      // On doit s'assurer d'avoir les types pour déterminer la catégorie
+      final types = List<String>.from(details['types'] ?? []);
+      final category = _determineCategoryFromTypes(types);
+
+      return await _convertPlaceToActivity(
+        details, // details a la structure nécessaire (geometry, name, etc)
+        tripId,
+        category,
+      );
+    } catch (e) {
+      LoggerService.error('ActivityPlacesService: Erreur get details: $e');
+      return null;
+    }
+  }
 }