feat: ajout d'un sélecteur de thèmes avec trois options (P'titsPas, Pastel, Sombre)

frontend/lib/screens/auth/login_screen.dart

@@ -1,6 +1,9 @@
 import 'package:flutter/material.dart';
 import 'package:go_router/go_router.dart';
 import '../../services/auth_service.dart';
+import '../../theme/theme_provider.dart';
+import '../../theme/app_theme.dart';
+import 'package:provider/provider.dart';
 
 class LoginScreen extends StatefulWidget {
   const LoginScreen({super.key});
@@ -15,6 +18,17 @@ class _LoginScreenState extends State<LoginScreen> {
   final _passwordController = TextEditingController();
   bool _isLoading = false;
 
+  String _getThemeName(ThemeType type) {
+    switch (type) {
+      case ThemeType.defaultTheme:
+        return "P'titsPas";
+      case ThemeType.pastelTheme:
+        return "Pastel";
+      case ThemeType.darkTheme:
+        return "Sombre";
+    }
+  }
+
   @override
   void dispose() {
     _emailController.dispose();
@@ -56,6 +70,29 @@ class _LoginScreenState extends State<LoginScreen> {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Connexion'),
+        actions: [
+          Consumer<ThemeProvider>(
+            builder: (context, themeProvider, child) {
+              return Padding(
+                padding: const EdgeInsets.symmetric(horizontal: 16.0),
+                child: DropdownButton<ThemeType>(
+                  value: themeProvider.currentTheme,
+                  items: ThemeType.values.map((ThemeType type) {
+                    return DropdownMenuItem<ThemeType>(
+                      value: type,
+                      child: Text(_getThemeName(type)),
+                    );
+                  }).toList(),
+                  onChanged: (ThemeType? newValue) {
+                    if (newValue != null) {
+                      themeProvider.setTheme(newValue);
+                    }
+                  },
+                ),
+              );
+            },
+          ),
+        ],
       ),
       body: Center(
         child: SingleChildScrollView(
@@ -105,11 +142,6 @@ class _LoginScreenState extends State<LoginScreen> {
                       : const Text('Se connecter'),
                 ),
                 const SizedBox(height: 16),
-                TextButton(
-                  onPressed: () => context.go('/register'),
-                  child: const Text('Créer un compte'),
-                ),
-                const SizedBox(height: 8),
                 TextButton(
                   onPressed: () => context.go('/parent-register'),
                   child: const Text('Créer un compte parent'),