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/components/moduleRegistry.tsx

@@ -4,7 +4,7 @@ import type { Page } from "../lib/urlState";
 import type { PanelId, PanelLayout } from "../lib/panelLayout";
 import Sidebar from "./Sidebar";
 import PlaylistsRail from "./PlaylistsRail";
-import { Feed, FeedPage, Messages, MessagesPage } from "./modulePages";
+import { Feed, FeedPage } from "./modulePages";
 
 // The RENDER half of the module registry: which component (and side rail) each page renders. The
 // metadata half — nav order, label, icon, gate — lives in lib/modules.ts (imported by NavSidebar /
@@ -54,7 +54,6 @@ export const PAGE_CONTENT: Record<Page, PageDef> = {
   playlists: { Component: Playlists, maxWidth: "64rem" },
   plex: { Component: PlexBrowse, maxWidth: "100rem" },
   notifications: { Component: NotificationsPanel, maxWidth: "48rem" },
-  messages: { Component: Object.assign(MessagesPage, { preload: Messages.preload }) },
   downloads: { Component: DownloadCenter, maxWidth: "56rem" },
   stats: { Component: Stats },
   scheduler: { Component: Scheduler },