feat(#44): UserManagementPanel + masquer onglet Administrateurs (dashboard gestionnaire)

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

frontend/lib/widgets/admin/dashboard_admin.dart

@@ -139,7 +139,8 @@ class DashboardAppBarAdmin extends StatelessWidget
   }
 }
 
-/// Sous-barre : Gestionnaires | Parents | Assistantes maternelles | Administrateurs.
+/// Sous-barre : Gestionnaires | Parents | Assistantes maternelles | [Administrateurs].
+/// [subTabCount] = 3 pour masquer l'onglet Administrateurs (dashboard gestionnaire).
 class DashboardUserManagementSubBar extends StatelessWidget {
   final int selectedSubIndex;
   final ValueChanged<int> onSubTabChange;
@@ -148,6 +149,14 @@ class DashboardUserManagementSubBar extends StatelessWidget {
   final Widget? filterControl;
   final VoidCallback? onAddPressed;
   final String addLabel;
+  final int subTabCount;
+
+  static const List<String> _tabLabels = [
+    'Gestionnaires',
+    'Parents',
+    'Assistantes maternelles',
+    'Administrateurs',
+  ];
 
   const DashboardUserManagementSubBar({
     Key? key,
@@ -158,6 +167,7 @@ class DashboardUserManagementSubBar extends StatelessWidget {
     this.filterControl,
     this.onAddPressed,
     this.addLabel = '+ Ajouter',
+    this.subTabCount = 4,
   }) : super(key: key);
 
   @override
@@ -171,13 +181,10 @@ class DashboardUserManagementSubBar extends StatelessWidget {
       padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 6),
       child: Row(
         children: [
-          _buildSubNavItem(context, 'Gestionnaires', 0),
-          const SizedBox(width: 12),
-          _buildSubNavItem(context, 'Parents', 1),
-          const SizedBox(width: 12),
-          _buildSubNavItem(context, 'Assistantes maternelles', 2),
-          const SizedBox(width: 12),
-          _buildSubNavItem(context, 'Administrateurs', 3),
+          for (int i = 0; i < subTabCount; i++) ...[
+            if (i > 0) const SizedBox(width: 12),
+            _buildSubNavItem(context, _tabLabels[i], i),
+          ],
           const SizedBox(width: 36),
           _pillField(
             width: 320,