The issues filter dropdown always rendered the label scope divider and
header, even when .ExclusiveLabelScopes was empty.
This PR wraps the label scope section with a conditional so the
divider/header and scope entries are only displayed when scopes exist.
Before
The dropdown showed a divider and “Label” header even when there were no
exclusive label scopes available.
<img width="521" height="569" alt="image"
src="https://github.com/user-attachments/assets/9766df6b-c11b-46f3-aabc-9fa5f4ca767d"
/>
After
The label scope section is hidden entirely when .ExclusiveLabelScopes is
empty, keeping the dropdown clean and consistent.
<img width="329" height="485" alt="image"
src="https://github.com/user-attachments/assets/e9586e57-2be5-43ea-8a13-9b87c951be6f"
/>
Notes
UI-only change, no behavior change to filtering logic.
ef9c19691d