fix: comprehensive security, bug, performance, and UI/UX audit

Security
- Default bind 127.0.0.1; first-run bootstrap generates random api_token
  and refuses to bind non-loopback without auth unless explicitly opted in
- Path-traversal hardened: BrowserService.validate_path rejects absolute
  paths, drive letters, UNC, NUL bytes. /api/browser/{play,metadata,
  thumbnail} now require folder_id and a folder-relative path
- Pydantic validators on links: http(s) URLs only, mdi:<slug> icons only
- Scripts/callbacks/links create/update/delete gated by *_management flags
- Strict CSP, X-Frame-Options DENY, Referrer-Policy no-referrer,
  X-Content-Type-Options nosniff
- CORS locked to localhost:<port> + 127.0.0.1:<port> by default; configurable
- config.yaml writes atomic (tmp + os.replace) and 0o600 on POSIX
- Subprocesses spawned in their own process group / new session so timeout
  kills the whole tree (Windows CREATE_NEW_PROCESS_GROUP, POSIX
  start_new_session=True)
- Frontend XSS: monitor name + details escapeHtml'd; power button moved to
  delegated data-action handler; remote MDI SVGs parsed and sanitized
  (strip script/foreignObject/on*/javascript: hrefs) before innerHTML
- All dynamic URL segments now wrapped in encodeURIComponent

Bugs
- WebSocket reconnect: close previous socket before opening new, clear
  ping interval per-socket, clear reconnectTimeout up-front, retry on
  online/visibilitychange, try/catch JSON.parse
- Artwork fetch race: AbortController + generation guard
- _broadcast_after_open: initialize status, swallow per-poll errors,
  background tasks tracked in a strong-ref set with done-callback cleanup
- Audio analyzer: sticky _unavailable flag prevents infinite start/stop
  spin when no loopback device exists; cleared by set_device()
- Volume short-circuit cache invalidated when server reports remote volume
- Browser thumbnail race: per-folder generation counter + isConnected
  checks; aborts in-flight fetches on navigation
- Track-skip uses cached title instead of full WinRT status round-trip

Performance
- Linux MPRIS/pactl and /api/display DDC-CI handlers wrapped in
  asyncio.to_thread so blocking IO never stalls the event loop
- browse_directory moved off the event loop (SMB shares could freeze it)
- Windows status poll caches one asyncio loop per worker thread via
  threading.local instead of new_event_loop/close on every 0.5s tick
- broadcast() serializes JSON once and uses send_text to all clients
- Hourly thumbnail cache cleanup scheduled in lifespan (was never invoked
  — cache grew unbounded)
- Progress drag listeners attached only while dragging

Quality
- All asyncio.get_event_loop() in coroutines → get_running_loop()
- ThreadPoolExecutors shut down cleanly during lifespan teardown
- config_manager dedup: 12 near-identical methods collapsed onto generic
  _upsert/_delete helpers (~290 lines removed)
- Service worker no longer pass-throughs every fetch
- M3U playlist written via NamedTemporaryFile (no fixed-path symlink
  clobber race)
- __version__ now prefers live pyproject.toml in dev checkouts so
  pip install -e . users see the source-of-truth version, not the stale
  package-metadata version baked in at install time

UI/UX (Studio Reference)
- Green leftover focus rings (rgba(29,185,84,...)) all replaced with
  copper accent (rgba(var(--copper-rgb),...))
- Dialogs: square corners, copper top hairline, unified with editorial
  chrome
- .browser-item: transparent with copper hover border (was filled card)
- Audio device select uses var(--sans) instead of generic system font
- Mobile container padding tuned for ≤480px screens
- Breadcrumb home is a real <button> with aria-label; aria-current on root
- i18n: filled display.msg.power_*, execution.*, scripts.params.execute,
  callbacks.empty in both en + ru

media_server/static/locales/en.json

@@ -174,6 +174,18 @@
   "display.msg.color_failed": "Failed to apply color preset",
   "display.msg.mode_changed": "Picture mode applied",
   "display.msg.mode_failed": "Failed to apply picture mode",
+  "display.msg.power_on": "Monitor turned on",
+  "display.msg.power_off": "Monitor turned off",
+  "display.msg.power_failed": "Failed to change monitor power",
+  "execution.result": "Execution Result",
+  "execution.executing": "Executing",
+  "execution.status": "Status",
+  "execution.exit_code": "Exit Code",
+  "execution.duration": "Duration",
+  "execution.success": "Success",
+  "execution.failed": "Failed",
+  "execution.running": "Running...",
+  "execution.no_output": "(no output)",
   "browser.title": "Media Browser",
   "browser.home": "Home",
   "browser.manage_folders": "Manage Folders",

media_server/static/locales/ru.json

@@ -174,6 +174,18 @@
   "display.msg.color_failed": "Не удалось применить цветовую температуру",
   "display.msg.mode_changed": "Режим изображения применён",
   "display.msg.mode_failed": "Не удалось применить режим изображения",
+  "display.msg.power_on": "Монитор включён",
+  "display.msg.power_off": "Монитор выключен",
+  "display.msg.power_failed": "Не удалось переключить питание монитора",
+  "execution.result": "Результат выполнения",
+  "execution.executing": "Выполняется",
+  "execution.status": "Статус",
+  "execution.exit_code": "Код выхода",
+  "execution.duration": "Длительность",
+  "execution.success": "Успешно",
+  "execution.failed": "Ошибка",
+  "execution.running": "Выполняется...",
+  "execution.no_output": "(нет вывода)",
   "browser.title": "Медиа Браузер",
   "browser.home": "Главная",
   "browser.manage_folders": "Управление папками",