feat: implement authentication flow with AppStartGate, AuthGuard, and calendar page initialization

em2rp/lib/utils/app_start_gate.dart

@@ -4,8 +4,9 @@ import 'package:provider/provider.dart';
 import 'dart:async';
 
 import '../views/login_page.dart';
-import '../utils/colors.dart';
+
 import '../providers/local_user_provider.dart';
+import '../views/widgets/common/startup_splash_screen.dart';
 
 /// Gate de démarrage qui attend la restauration Firebase Auth avant
 /// d'afficher soit le contenu connecté, soit la page de connexion.
@@ -43,14 +44,14 @@ class AppStartGate extends StatelessWidget {
       stream: safeAuthStream,
       builder: (context, snapshot) {
         if (snapshot.connectionState == ConnectionState.waiting) {
-          return const _StartupSplashScreen();
+          return const StartupSplashScreen();
         }
 
         if (snapshot.hasError) {
           // En théorie handleError évite d'arriver ici, mais on garde
           // une protection supplémentaire.
           debugPrint('[AppStartGate] snapshot error: ${snapshot.error}');
-          return const _StartupSplashScreen(message: 'Erreur de connexion');
+          return const StartupSplashScreen(message: 'Erreur de connexion');
         }
 
         if (snapshot.data != null) {
@@ -101,44 +102,9 @@ class _AuthenticatedBootstrapState extends State<_AuthenticatedBootstrap> {
 
   @override
   Widget build(BuildContext context) {
-    return const _StartupSplashScreen();
+    return const StartupSplashScreen();
   }
 }
 
-class _StartupSplashScreen extends StatelessWidget {
-  final String message;
 
-  const _StartupSplashScreen({this.message = 'Démarrage...'});
-
-  @override
-  Widget build(BuildContext context) {
-    return Scaffold(
-      backgroundColor: Colors.white,
-      body: Center(
-        child: Column(
-          mainAxisAlignment: MainAxisAlignment.center,
-          children: [
-            Image.asset(
-              'assets/logos/RectangleLogoBlack.png',
-              width: 160,
-              height: 160,
-              fit: BoxFit.contain,
-              errorBuilder: (context, error, stackTrace) {
-                return const Icon(
-                  Icons.event_available,
-                  size: 72,
-                  color: AppColors.rouge,
-                );
-              },
-            ),
-            const SizedBox(height: 24),
-            const CircularProgressIndicator(),
-            const SizedBox(height: 16),
-            Text(message),
-          ],
-        ),
-      ),
-    );
-  }
-}