feat(client): LT Wahl admin, Teamer admin, Verantwortlichen self-registration

New screens (client/app/lib/screens/):
- wahl_admin_screen.dart — per KC: list/create Wahlen; per Wahl: add
  workshops, run the assignment (POST /wahl/:id/zuteilung/run), view the
  result table.
- teamer_admin_screen.dart — per Gemeinde: list/create local Teamer
  accounts, create group-link or per-email invites (shows the token).
- verantwortliche_register_screen.dart — enter a KC invite code
  (GET /onboarding/kc/:code), pick a Gemeinde, submit
  (POST /onboarding/verantwortliche); shown on the home screen to a
  logged-in Authentik user who has no membership yet.
- ui.dart — shared toast / ErrorText / SectionHeader / promptText.
KcDetailScreen now links to Wahl admin and each Gemeinde row opens Teamer
admin.

Backend: widen the wahl + files LT routes to AuthGuard(['authentik','team'])
for consistency with the other LT controllers. Rebrand web/index.html +
manifest from "kc_app" to "KC-App".

Verified against local Postgres with an isLeitungsteam team token: create
KC/Gemeinde/Wahl/Workshop, run Zuteilung, create Teamer + invite, resolve
an invite code. flutter analyze/test/build web green; backend npm test 56.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

client/app/lib/screens/admin_screen.dart

@@ -2,6 +2,9 @@ import 'package:flutter/material.dart';
 
 import '../api.dart';
 import '../main.dart';
+import 'teamer_admin_screen.dart';
+import 'ui.dart';
+import 'wahl_admin_screen.dart';
 
 /// Leitungsteam admin: KCs, their Gemeinden, and pending self-registrations.
 class AdminScreen extends StatefulWidget {
@@ -24,13 +27,13 @@ class _AdminScreenState extends State<AdminScreen> {
 
   Future<void> _createKc() async {
     final api = AppScope.of(context).api;
-    final name = await _promptText(context, 'Neues KC', 'Name');
+    final name = await promptText(context, 'Neues KC', 'Name');
     if (name == null || name.isEmpty || !mounted) return;
     try {
       await api.createKc(name);
       if (mounted) _reload();
     } catch (e) {
-      if (mounted) _toast(context, '$e');
+      if (mounted) toast(context, '$e');
     }
   }
 
@@ -109,13 +112,13 @@ class _KcDetailScreenState extends State<KcDetailScreen> {
 
   Future<void> _addGemeinde() async {
     final api = _api;
-    final name = await _promptText(context, 'Neue Gemeinde', 'Name');
+    final name = await promptText(context, 'Neue Gemeinde', 'Name');
     if (name == null || name.isEmpty || !mounted) return;
     try {
       await api.createGemeinde(widget.kc.id, name);
       if (mounted) _reloadGemeinden();
     } catch (e) {
-      if (mounted) _toast(context, '$e');
+      if (mounted) toast(context, '$e');
     }
   }
 
@@ -133,20 +136,22 @@ class _KcDetailScreenState extends State<KcDetailScreen> {
               trailing: const Icon(Icons.qr_code_2),
             ),
           ),
-          const SizedBox(height: 16),
-          Row(
-            children: [
-              Expanded(
-                child: Text('Gemeinden',
-                    style: Theme.of(context).textTheme.titleMedium),
+          Card(
+            child: ListTile(
+              leading: const Icon(Icons.how_to_vote),
+              title: const Text('Workshop-Wahlen'),
+              trailing: const Icon(Icons.chevron_right),
+              onTap: () => Navigator.of(context).push(
+                MaterialPageRoute(builder: (_) => WahlAdminScreen(kcId: widget.kc.id)),
               ),
-              TextButton.icon(
-                onPressed: _addGemeinde,
-                icon: const Icon(Icons.add),
-                label: const Text('Hinzufügen'),
-              ),
-            ],
+            ),
           ),
+          const SizedBox(height: 16),
+          SectionHeader('Gemeinden', action: TextButton.icon(
+            onPressed: _addGemeinde,
+            icon: const Icon(Icons.add),
+            label: const Text('Hinzufügen'),
+          )),
           _GemeindeList(future: _gemeinden!, onRetry: _reloadGemeinden),
           const Divider(height: 40),
           Text('Offene Verantwortlichen-Anfragen',
@@ -161,7 +166,7 @@ class _KcDetailScreenState extends State<KcDetailScreen> {
                     : await _api.rejectOnboarding(id);
                 _reloadRequests();
               } catch (e) {
-                if (context.mounted) _toast(context, '$e');
+                if (context.mounted) toast(context, '$e');
               }
             },
           ),
@@ -199,6 +204,12 @@ class _GemeindeList extends StatelessWidget {
                 dense: true,
                 leading: const Icon(Icons.church),
                 title: Text(g.name),
+                trailing: const Icon(Icons.chevron_right),
+                onTap: () => Navigator.of(context).push(
+                  MaterialPageRoute(
+                    builder: (_) => TeamerAdminScreen(gemeindeId: g.id, gemeindeName: g.name),
+                  ),
+                ),
               ),
           ],
         );
@@ -260,32 +271,3 @@ class _RequestList extends StatelessWidget {
   }
 }
 
-Future<String?> _promptText(BuildContext context, String title, String label) {
-  final controller = TextEditingController();
-  return showDialog<String>(
-    context: context,
-    builder: (context) => AlertDialog(
-      title: Text(title),
-      content: TextField(
-        controller: controller,
-        autofocus: true,
-        decoration: InputDecoration(labelText: label),
-        onSubmitted: (v) => Navigator.of(context).pop(v.trim()),
-      ),
-      actions: [
-        TextButton(
-          onPressed: () => Navigator.of(context).pop(),
-          child: const Text('Abbrechen'),
-        ),
-        FilledButton(
-          onPressed: () => Navigator.of(context).pop(controller.text.trim()),
-          child: const Text('OK'),
-        ),
-      ],
-    ),
-  );
-}
-
-void _toast(BuildContext context, String message) {
-  ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(message)));
-}