Summary

Part of #8635 — removes the last antd dependency from project settings pages.

Changes

• Replace antd Select with @highlight-run/ui ComboboxSelect in GitHubSettingsModal.tsx
• Maintains search/filter functionality via ComboboxSelect built-in search
• Uses existing highlight-run/ui components consistently
• Single file, minimal change (1 file, -17/+15 lines)

How did you test this change?

Verified the component API mapping:

• showSearch + filterOption → ComboboxSelect has built-in search
• onSelect → onChange
• notFoundContent → emptyStateRender
• options format updated from {id, label, value} to {key, render}

Are there any deployment considerations?

No. Frontend-only, single component swap.

/claim #8635