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/push_subject.dart

@@ -1,3 +1,42 @@
+/// Parsed parts of a Talk push subject text.
+///
+/// Format verified against nextcloud/spreed `Notifier::parseChatMessage`:
+/// with message preview the parsed subject is `"{user}\n{message}"` for 1:1
+/// chats and `'{user} in {call}' . "\n{message}"` for groups — header and
+/// message are separated by a NEWLINE, and the notifications app forwards the
+/// parsed subject unmodified (only shortened). The German translation of
+/// `{user} in {call}` is identical (`l10n/de.json`), so the ` in ` separator
+/// holds for de_DE. Legacy/other variants using `": "` are kept as fallback;
+/// splitting the header at the LAST ` in ` is robust against sender names
+/// containing "in" (only a display name literally containing ` in ` in a 1:1
+/// chat would still mis-split — accepted heuristic limit).
+({String sender, String? roomName, String text}) parseTalkSubject(String raw) {
+  String header;
+  String text;
+  final newline = raw.indexOf('\n');
+  if (newline > 0) {
+    header = raw.substring(0, newline).trim();
+    text = raw.substring(newline + 1);
+  } else {
+    final colon = raw.indexOf(': ');
+    if (colon > 0 && colon < raw.length - 2) {
+      header = raw.substring(0, colon);
+      text = raw.substring(colon + 2);
+    } else {
+      return (sender: 'Talk', roomName: null, text: raw);
+    }
+  }
+  final roomSep = header.lastIndexOf(' in ');
+  if (roomSep > 0 && roomSep + 4 < header.length) {
+    return (
+      sender: header.substring(0, roomSep),
+      roomName: header.substring(roomSep + 4),
+      text: text,
+    );
+  }
+  return (sender: header, roomName: null, text: text);
+}
+
 /// The decrypted `subject` JSON of a Nextcloud push-v2 notification.
 ///
 /// Covers the full shape the notifications app emits, including the three