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/routes/browser.py

@@ -328,7 +328,7 @@ async def get_thumbnail(
         thumbnail_data = await ThumbnailService.get_thumbnail(file_path, size)
 
         if thumbnail_data is None:
-            raise HTTPException(status_code=404, detail="Thumbnail not available")
+            return Response(status_code=204)
 
         # Calculate ETag (hash of path + mtime)
         import hashlib