feat(#145): lien co-parent cliquable dans la fiche parent.

Même UX que les responsables de la fiche enfant : ouverture de
AdminParentEditModal au clic sur le nom du co-parent.

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

frontend/lib/widgets/admin/common/admin_parent_edit_modal.dart

@@ -113,10 +113,73 @@ class _AdminParentEditModalState extends State<AdminParentEditModal> {
     return '$fn $ln'.trim();
   }
 
-  String? _coParentSubtitle() {
+  String? _coParentName() {
     final name = _coParent?.fullName.trim() ?? '';
-    if (name.isEmpty) return null;
+    return name.isEmpty ? null : name;
-    return 'Co-parent : $name';
+  }
+
+  Future<void> _openCoParent() async {
+    if (_saving) return;
+    final co = _coParent;
+    final id = (co?.id ?? '').trim();
+    if (co == null || id.isEmpty) return;
+
+    try {
+      final parent = await UserService.getParent(id);
+      if (!mounted) return;
+      await showDialog<void>(
+        context: context,
+        builder: (ctx) => AdminParentEditModal(
+          parent: parent,
+          onSaved: () async {
+            try {
+              final refreshed = await UserService.getParent(widget.parent.user.id);
+              if (!mounted) return;
+              setState(() => _coParent = refreshed.coParent);
+            } catch (_) {}
+            widget.onSaved?.call();
+          },
+        ),
+      );
+    } catch (e) {
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(e.toString().replaceFirst('Exception: ', ''))),
+      );
+    }
+  }
+
+  Widget? _coParentSubtitle() {
+    final name = _coParentName();
+    if (name == null) return null;
+
+    return Wrap(
+      crossAxisAlignment: WrapCrossAlignment.center,
+      children: [
+        const Text(
+          'Co-parent : ',
+          style: TextStyle(fontSize: 13, color: Colors.black54),
+        ),
+        InkWell(
+          onTap: _saving ? null : _openCoParent,
+          borderRadius: BorderRadius.circular(4),
+          child: Padding(
+            padding: const EdgeInsets.symmetric(horizontal: 2, vertical: 2),
+            child: Text(
+              name,
+              style: TextStyle(
+                fontSize: 13,
+                fontWeight: FontWeight.w600,
+                color: ValidationModalTheme.primaryActionBackground,
+                decoration: TextDecoration.underline,
+                decorationColor: ValidationModalTheme.primaryActionBackground
+                    .withValues(alpha: 0.5),
+              ),
+            ),
+          ),
+        ),
+      ],
+    );
   }
 
   Future<void> _save() async {
@@ -395,13 +458,7 @@ class _AdminParentEditModalState extends State<AdminParentEditModal> {
                         ),
                         if (_coParentSubtitle() != null) ...[
                           const SizedBox(height: 4),
-                          Text(
+                          _coParentSubtitle()!,
-                            _coParentSubtitle()!,
-                            style: const TextStyle(
-                              fontSize: 13,
-                              color: Colors.black54,
-                            ),
-                          ),
                         ],
                       ],
                     ),