feat(desktop): mention notifications via realtime + osNotify

apps/desktop/src/components/AppShell.tsx

@@ -6,6 +6,7 @@ import { startConversationKeySync } from '../lib/conversationKeySync';
 import { startDeviceApprovalListener } from '../lib/deviceApproval';
 import { ensureInstallId } from '../lib/installId';
 import { ensureNotificationPermission } from '../lib/osNotify';
+import { useMentionNotifications } from '../lib/useMentionNotifications';
 import { cachedUserKey } from '../lib/userIdentity';
 import { CallUI } from './CallUI';
 import { DeviceApprovalBanner } from './DeviceApprovalBanner';
@@ -13,6 +14,7 @@ import { Sidebar } from './Sidebar';
 
 export function AppShell() {
   const { session } = useAuth();
+  useMentionNotifications(session?.user.id);
   useEffect(() => {
     // Prompt once per authenticated shell mount. Module-level guard prevents
     // re-asking if the user already responded this session.

apps/desktop/src/lib/useMentionNotifications.ts

@@ -0,0 +1,45 @@
+import { useEffect } from 'react';
+
+import { notify } from './osNotify';
+import { supabase } from './supabase';
+
+interface MentionRow {
+  message_id: string;
+  mentioned_user_id: string;
+  conversation_id: string;
+}
+
+// Subscribes to my own message_mentions inserts and fires an OS notification
+// for each one. Bypasses per-conv mute (mentions override mute by design).
+//
+// We don't decrypt the body here — the notification just says "Du wurdest
+// erwähnt". The conv list highlight + the in-app navigation reveal context.
+export function useMentionNotifications(userId: string | undefined): void {
+  useEffect(() => {
+    if (!userId) return;
+    const channel = supabase
+      .channel('mentions:' + userId)
+      .on(
+        'postgres_changes',
+        {
+          event: 'INSERT',
+          schema: 'public',
+          table: 'message_mentions',
+          filter: 'mentioned_user_id=eq.' + userId,
+        },
+        (payload) => {
+          const row = payload.new as MentionRow | null;
+          if (!row) return;
+          void notify({
+            title: 'Du wurdest erwähnt',
+            body: 'Tippe um die Nachricht zu lesen.',
+            force: true,
+          });
+        },
+      )
+      .subscribe();
+    return () => {
+      void supabase.removeChannel(channel);
+    };
+  }, [userId]);
+}