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/navigation/main_navigation_layout.dart

@@ -118,7 +118,7 @@ class _MainNavigationLayoutState extends State<MainNavigationLayout> {
             statusBarIconBrightness: Brightness.dark,
           ),
           child: Scaffold(
-            backgroundColor: ColorTokens.background,
+            backgroundColor: Theme.of(context).scaffoldBackgroundColor,
             body: SafeArea(
               top: true,
               bottom: false,
@@ -199,12 +199,13 @@ class _PillNavigationBar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final scheme = Theme.of(context).colorScheme;
     return Container(
       decoration: BoxDecoration(
-        color: ColorTokens.surface,
+        color: scheme.surface,
         boxShadow: [
           BoxShadow(
-            color: ColorTokens.shadow,
+            color: scheme.shadow.withOpacity(0.12),
             blurRadius: 12,
             offset: const Offset(0, -2),
           ),