Update Web UI: Header redesign, thumbnail fix, and title fallback

- Add version label next to Media Server header (fetched from /api/health)
- Move connection status dot before title, remove status text
- Move logout button into header after language selector
- Return 204 instead of 404 for missing thumbnails (eliminates console errors)
- Show "Title unavailable" when media is playing but title is empty
- Add player.title_unavailable translation key for en/ru locales

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

media_server/static/locales/en.json

@@ -18,6 +18,7 @@
   "player.status.connected": "Connected",
   "player.status.disconnected": "Disconnected",
   "player.no_media": "No media playing",
+  "player.title_unavailable": "Title unavailable",
   "player.source": "Source:",
   "player.unknown_source": "Unknown",
   "state.playing": "Playing",

media_server/static/locales/ru.json

@@ -18,6 +18,7 @@
   "player.status.connected": "Подключено",
   "player.status.disconnected": "Отключено",
   "player.no_media": "Медиа не воспроизводится",
+  "player.title_unavailable": "Название недоступно",
   "player.source": "Источник:",
   "player.unknown_source": "Неизвестно",
   "state.playing": "Воспроизведение",