feat: livrer ticket #93 et finaliser #17 avec gestion des Relais (#95)

Homogénéise le dashboard admin (onglets/listes/cartes/états) via composants réutilisables, finalise la création gestionnaire côté backend, et intègre la gestion des Relais avec rattachement gestionnaire.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/lib/services/api/api_config.dart

@@ -18,11 +18,13 @@ class ApiConfig {
   static const String gestionnaires = '/gestionnaires';
   static const String parents = '/parents';
   static const String assistantesMaternelles = '/assistantes-maternelles';
+  static const String relais = '/relais';
 
   // Configuration (admin)
   static const String configuration = '/configuration';
   static const String configurationSetupStatus = '/configuration/setup/status';
-  static const String configurationSetupComplete = '/configuration/setup/complete';
+  static const String configurationSetupComplete =
+      '/configuration/setup/complete';
   static const String configurationTestSmtp = '/configuration/test-smtp';
   static const String configurationBulk = '/configuration/bulk';
 
@@ -33,14 +35,14 @@ class ApiConfig {
   static const String conversations = '/conversations';
   static const String notifications = '/notifications';
 
-   // Headers
+  // Headers
   static Map<String, String> get headers => {
-    'Content-Type': 'application/json',
-    'Accept': 'application/json',
-  };
+        'Content-Type': 'application/json',
+        'Accept': 'application/json',
+      };
 
   static Map<String, String> authHeaders(String token) => {
-    ...headers,
-    'Authorization': 'Bearer $token',
-  };
-}
+        ...headers,
+        'Authorization': 'Bearer $token',
+      };
+}