feat(#95): implémenter la gestion Relais admin et le rattachement gestionnaire

Ajoute la section Paramètres territoriaux avec CRUD Relais, modale de saisie structurée, états visuels harmonisés, et rattachement d'un relais principal aux gestionnaires via l'API.

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',
+      };
+}