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/lib/keymap.ts

@@ -116,7 +116,6 @@ export const SHORTCUTS = [
     labelKey: "keys.goNotifications",
     page: "notifications",
   },
-  { id: "goMessages", scope: "page", keys: ["g m"], labelKey: "keys.goMessages", page: "messages" },
   {
     id: "goDownloads",
     scope: "page",