implemented dual Nextcloud push registration with separate general and talk apptypes to ensure reliable Talk notification delivery; introduced stacked MessagingStyle notifications for chat threads with support for circular conversation avatars and disk caching

lib/push/nextcloud_push_api.dart

@@ -39,17 +39,24 @@ class NextcloudPushApi {
 
   NextcloudPushApi({http.Client? client}) : _client = client ?? http.Client();
 
-  /// Registers (or refreshes) this device. [devicePublicKeyPem] must be the
-  /// 64-column SPKI PEM. [proxyServer] is the MarianumConnect push-proxy base
-  /// URL (with trailing slash).
+  /// Registers (or refreshes) a device subscription. [devicePublicKeyPem] must
+  /// be the 64-column SPKI PEM. [proxyServer] is the MarianumConnect push-proxy
+  /// base URL (with trailing slash).
+  ///
+  /// [authorizationHeader] overrides the Basic auth (e.g. the Talk app
+  /// password — NC binds the subscription to the authenticated session token).
+  /// [userAgent] overrides the UA; a Talk-pattern UA makes NC classify the
+  /// subscription as apptype `talk` and route Talk pushes to it.
   Future<NextcloudPushRegistration> register({
     required String pushTokenHash,
     required String devicePublicKeyPem,
     required String proxyServer,
+    String? authorizationHeader,
+    String? userAgent,
   }) async {
     final response = await _client.post(
       NextcloudOcs.uri(_path),
-      headers: NextcloudOcs.headers(),
+      headers: _headers(authorizationHeader, userAgent),
       body: {
         'pushTokenHash': pushTokenHash,
         'devicePublicKey': devicePublicKeyPem,
@@ -76,13 +83,24 @@ class NextcloudPushApi {
     );
   }
 
-  /// Unregisters this device from Nextcloud push. Returns true when the server
-  /// responded 202, meaning the proxy subscription should also be removed.
-  Future<bool> unregister() async {
+  /// Unregisters one device subscription — the DELETE is per session token, so
+  /// each registration is removed with its own app password via
+  /// [authorizationHeader]. Returns true when the server responded 202,
+  /// meaning the proxy subscription should also be removed.
+  Future<bool> unregister({String? authorizationHeader}) async {
     final response = await _client.delete(
       NextcloudOcs.uri(_path),
-      headers: NextcloudOcs.headers(),
+      headers: _headers(authorizationHeader, null),
     );
     return response.statusCode == 202;
   }
+
+  Map<String, String> _headers(
+    String? authorizationHeader,
+    String? userAgent,
+  ) => {
+    ...NextcloudOcs.headers(),
+    'Authorization': ?authorizationHeader,
+    'User-Agent': ?userAgent,
+  };
 }