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>

src/i18n/locales/de/settings.json

@@ -91,7 +91,6 @@
     "git": "Git",
     "apiTokens": "API & Token",
     "tasks": "Aufgaben",
-    "computer": "Computer Use",
     "notifications": "Benachrichtigungen",
     "plugins": "Plugins",
     "about": "Info"

src/i18n/locales/en/settings.json

@@ -110,7 +110,6 @@
     "voice": "Voice",
     "tasks": "Tasks",
     "browser": "Browser",
-    "computer": "Computer Use",
     "notifications": "Notifications",
     "plugins": "Plugins",
     "about": "About"

src/i18n/locales/fr/settings.json

@@ -91,7 +91,6 @@
     "git": "Git",
     "apiTokens": "API & Tokens",
     "tasks": "Tâches",
-    "computer": "Computer Use",
     "notifications": "Notifications",
     "plugins": "Plugins",
     "about": "À propos"

src/i18n/locales/it/settings.json

@@ -91,7 +91,6 @@
     "git": "Git",
     "apiTokens": "API e Token",
     "tasks": "Attività",
-    "computer": "Computer Use",
     "notifications": "Notifiche",
     "plugins": "Plugin",
     "about": "Informazioni"

src/i18n/locales/ja/settings.json

@@ -91,7 +91,6 @@
     "git": "Git",
     "apiTokens": "API & トークン",
     "tasks": "タスク",
-    "computer": "Computer Use",
     "notifications": "通知",
     "plugins": "プラグイン",
     "about": "概要"

src/i18n/locales/ko/settings.json

@@ -91,7 +91,6 @@
     "git": "Git",
     "apiTokens": "API & 토큰",
     "tasks": "작업",
-    "computer": "Computer Use",
     "notifications": "알림",
     "plugins": "플러그인",
     "about": "정보"

src/i18n/locales/ru/settings.json

@@ -91,7 +91,6 @@
     "git": "Git",
     "apiTokens": "API и токены",
     "tasks": "Задачи",
-    "computer": "Computer Use",
     "notifications": "Уведомления",
     "plugins": "Плагины",
     "about": "О программе"