Improve error handling for unavailable network shares

- Add OSError/PermissionError handling in browse endpoint
- Return 503 status code when folders are temporarily unavailable
- Display user-friendly error messages in the UI
- Enhance error logging with exception type information

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

media_server/routes/browser.py

@@ -254,8 +254,15 @@ async def browse(
         raise HTTPException(status_code=400, detail=str(e))
     except FileNotFoundError as e:
         raise HTTPException(status_code=404, detail=str(e))
+    except (OSError, PermissionError) as e:
+        # Network share unavailable or access denied
+        logger.warning(f"Folder temporarily unavailable: {e}")
+        raise HTTPException(
+            status_code=503,
+            detail=f"Folder is temporarily unavailable. It may be a network share that is not accessible at the moment."
+        )
     except Exception as e:
-        logger.error(f"Error browsing directory: {e}")
+        logger.error(f"Error browsing directory (type: {type(e).__name__}): {e}")
         raise HTTPException(status_code=500, detail="Failed to browse directory")