feat!: remove direct messaging (chat)

E2EE direct messages, the chat dock, the Messages module, the message
WebSocket and its realtime registry, and the messages / message_keys
tables (migration 0097; the downgrade restores the empty schema). Prod
held two welcome notes, no message between people and one key — never
used (owner decision, E34). WebSocket now has no owner module: the lint
bans it everywhere. Privacy policy updated: it no longer promises E2EE
for a feature that is gone.

frontend/src/design-lab/batchB.tsx

@@ -9,7 +9,6 @@ import {
   Home,
   ListVideo,
   Lock,
-  MessageSquare,
   PlayCircle,
   Repeat,
   Settings,
@@ -290,7 +289,6 @@ const NAV: NavDef[] = [
   { icon: ListVideo, en: "Playlists", hu: "Listák" },
   { icon: Clapperboard, en: "Plex", hu: "Plex" },
   { icon: Bell, en: "Alerts", hu: "Értesítés" },
-  { icon: MessageSquare, en: "Messages", hu: "Üzenetek" },
   { icon: Download, en: "Downloads", hu: "Letöltések" },
 ];
 const SYSTEM: NavDef[] = [