fix: address review feedback for ParalinguisticInput

- Initialize lastSerializedRef to empty string so first-mount hydration
  always runs (fixes initial value not rendering)
- Guard arrow-key menu nav against empty filteredTags (avoids NaN index)
- Disable ARIA role/multiline and detach event handlers when disabled
- Add onBlur to close autocomplete dropdown when editor loses focus
- Chain exception with 'from e' in unload endpoint for better tracebacks

backend/main.py

@@ -1546,7 +1546,7 @@ async def unload_model_by_name(model_name: str):
 
         return {"message": f"Model {model_name} unloaded successfully"}
     except Exception as e:
-        raise HTTPException(status_code=500, detail=str(e))
+        raise HTTPException(status_code=500, detail=str(e)) from e
 
 
 @app.get("/models/progress/{model_name}")