feat(core): refonte architecture transverse (cache, network, websocket, DI)

- lib/app : app.dart, router mis à jour (routes nouveaux modules)
- lib/core/cache : cache_service + cached_datasource_decorator
- lib/core/network : api_client, offline_manager, retry_policy
- lib/core/websocket : websocket service (reconnexion exponentielle, heartbeat)
- lib/core/di : injection + register_module
- lib/core/storage : pending_operations_store (offline support)
- lib/core/navigation : main_navigation_layout (onglets par rôle)
- lib/core/config : environment, lcb_ft_constants
- lib/core/utils : error_formatter, validators
- pubspec.yaml/lock : dépendances mises à jour

lib/core/websocket/websocket_service.dart

@@ -77,6 +77,17 @@ abstract class WebSocketEvent {
           organizationId: json['organizationId'] as String?,
         );
 
+      case 'NOUVEAU_MESSAGE':
+      case 'MESSAGE_SUPPRIME':
+      case 'CONVERSATION_LUE':
+        return ChatMessageEvent(
+          eventType: eventType,
+          timestamp: timestamp,
+          data: data,
+          conversationId: json['conversationId'] as String?,
+          organizationId: json['organizationId'] as String?,
+        );
+
       default:
         return GenericEvent(
           eventType: eventType,
@@ -144,6 +155,19 @@ class ContributionEvent extends WebSocketEvent {
   });
 }
 
+class ChatMessageEvent extends WebSocketEvent {
+  final String? conversationId;
+  final String? organizationId;
+
+  ChatMessageEvent({
+    required super.eventType,
+    required super.timestamp,
+    required super.data,
+    this.conversationId,
+    this.organizationId,
+  });
+}
+
 class GenericEvent extends WebSocketEvent {
   GenericEvent({
     required super.eventType,