feat: Wahl result view + live WebSocket chat in the Flutter client

Backend:
- fix(chat): ChatGateway stored the per-socket caller only after the async
  token check resolved, so a client that sent chat:join immediately on open
  raced ahead and got 4001. The caller is now stored as a promise that the
  message handlers await. Verified with a two-client send/receive E2E test
  against local Postgres.

Client (client/app/):
- Wahl screen gains a "Ergebnis" tab backed by GET /wahl/guest/results
  (PENDING / ASSIGNED with workshop + wish rank / UNASSIGNED).
- Chat channel view loads history over REST, then connects the /chat
  WebSocket (chat_socket.dart): live chat:message stream + a compose bar
  that sends chat:send. Shows the socket status.
- web_socket_channel dependency added.

flutter analyze/test/build web all green; backend npm test 56.

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

client/app/lib/api.dart

@@ -145,6 +145,44 @@ class GuestOverview {
       );
 }
 
+enum WahlResultStatus { pending, assigned, unassigned }
+
+class WahlResult {
+  WahlResult({
+    required this.wahlName,
+    required this.datumsSchluessel,
+    required this.teil,
+    required this.status,
+    required this.workshopName,
+    required this.wunschRang,
+    required this.isForced,
+  });
+  final String wahlName;
+  final String datumsSchluessel;
+  final String teil;
+  final WahlResultStatus status;
+  final String? workshopName;
+  final int? wunschRang;
+  final bool isForced;
+
+  factory WahlResult.fromJson(Map<String, dynamic> j) {
+    final wahl = j['wahl'] as Map<String, dynamic>;
+    return WahlResult(
+      wahlName: wahl['name'] as String,
+      datumsSchluessel: wahl['datumsSchluessel'] as String,
+      teil: wahl['teil'] as String,
+      status: switch (j['status'] as String?) {
+        'ASSIGNED' => WahlResultStatus.assigned,
+        'UNASSIGNED' => WahlResultStatus.unassigned,
+        _ => WahlResultStatus.pending,
+      },
+      workshopName: j['workshopName'] as String?,
+      wunschRang: (j['wunschRang'] as num?)?.toInt(),
+      isForced: j['isForced'] as bool? ?? false,
+    );
+  }
+}
+
 class FileEntry {
   FileEntry({required this.id, required this.filename, required this.visibility});
   final String id;
@@ -262,6 +300,11 @@ class Api {
     await _post('/wahl/$wahlId/teilnehmer', {'prioritaeten': workshopIds});
   }
 
+  Future<List<WahlResult>> guestWahlResults() async {
+    final list = await _get('/wahl/guest/results') as List<dynamic>;
+    return list.map((e) => WahlResult.fromJson(e as Map<String, dynamic>)).toList();
+  }
+
   // --- files ---
   Future<List<FileEntry>> files(String kcId) async {
     final list = await _get('/files/$kcId') as List<dynamic>;
@@ -270,6 +313,19 @@ class Api {
 
   String fileDownloadUrl(String fileId) => '$kApiBase/files/download/$fileId';
 
+  /// WebSocket endpoint for the chat gateway. It lives at `/chat` (outside the
+  /// `/api` prefix) and authenticates via a `?token=` query param.
+  Uri chatWsUri() {
+    final base = Uri.parse(kApiBase);
+    return Uri(
+      scheme: base.scheme == 'https' ? 'wss' : 'ws',
+      host: base.host,
+      port: base.hasPort ? base.port : null,
+      path: '/chat',
+      queryParameters: {'token': token ?? ''},
+    );
+  }
+
   // --- chat (read-only for now; sending is a WebSocket-only path) ---
   Future<List<ChatChannel>> channels(String kcId) async {
     final list = await _get('/chat/$kcId/channels') as List<dynamic>;