- Add @tanstack/react-query and wire up QueryClientProvider in App.tsx
- Refactor BranchToolbar to use useQuery for branch listing and
  useMutation for checkout, create branch, and git init, replacing
  manual useState/useCallback/useEffect async patterns
- Fix branch sync effect and ChatView envMode effect to use stable
  primitive deps instead of full object references, preventing
  unnecessary re-runs on unrelated store dispatches

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>