chore: remove computer use (re-applied after main merge)

The merge of main into this branch (0907d87) hit a modify/delete conflict
for the computer-use module — main removed it in 6761f31 while this branch
had extended it — and the conflict was resolved by keeping the branch's
copies, silently resurrecting the whole feature.

This re-applies 6761f31's removal on top of the browser-use work:
- deletes the computer-use server module, client panel, settings tab,
  desktop-agent websocket service, electron computerAgent, and the
  computer-semantics build scripts
- strips computer-use wiring from shared files (server/index.js, electron
  launcher/main, MainContent, settings, i18n) while preserving browser-use
- removes src/constants/featureFlags.ts (existed only for the CU menu flag)

browser-use (camoufox/noVNC) is untouched. typecheck passes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/modules/websocket/services/websocket-server.service.ts

@@ -7,7 +7,6 @@ import { VIEWER_COOKIE_NAME } from '@/modules/browser-use/index.js';
 import { verifyWebSocketClient } from '@/modules/websocket/services/websocket-auth.service.js';
 import { handlePluginWsProxy } from '@/modules/websocket/services/plugin-websocket-proxy.service.js';
 import { handleShellConnection } from '@/modules/websocket/services/shell-websocket.service.js';
-import { handleDesktopAgentConnection } from '@/modules/websocket/services/desktop-agent-websocket.service.js';
 import { handleDesktopNotificationsConnection } from '@/modules/notifications/index.js';
 import type { AuthenticatedWebSocketRequest } from '@/shared/types.js';
 
@@ -89,11 +88,6 @@ export function createWebSocketServer(
       return;
     }
 
-    if (pathname === '/desktop-agent') {
-      handleDesktopAgentConnection(ws, incomingRequest);
-      return;
-    }
-
     if (pathname === '/desktop-notifications') {
       handleDesktopNotificationsConnection(ws, incomingRequest);
       return;