Add loading feedback to git changes refresh button

[amanape]

Problem

When clicking the refresh button in the Changes tab, there is no visual feedback indicating that the git changes API is being called. Users have no way to know if their click was registered or if data is being fetched, which can lead to confusion and repeated clicks.

Expected Behavior

The refresh button should provide clear visual feedback when a refresh is in progress. The button should appear in a loading state and prevent additional clicks until the current fetch completes.

Acceptance Criteria

• The refresh icon should spin while the git changes API request is in progress.
• The button should be disabled during loading to prevent multiple simultaneous requests.
• The button should have a visually distinct appearance when disabled, such as reduced opacity.
• Consider using isFetching from TanStack Query rather than isLoading, since isLoading only applies to the initial load while isFetching covers refetch scenarios. (see https://stackoverflow.com/questions/75401477/reasons-for-using-isloading-or-isfetching-in-react-query)

Relevant Files

• frontend/src/components/features/conversation/conversation-tabs/conversation-tab-title.tsx contains the refresh button component that needs the loading state.
• frontend/src/hooks/query/use-unified-get-git-changes.ts contains the hook that fetches git changes and will need to expose isFetching.

[github-actions]

🙌 Hey there, future contributor! 🙌

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[sameer1sheikh2mansoori3]

@amanape can you please review my pr ?