Add API client with React Query integration
- Install axios and @tanstack/react-query
- Create TypeScript types for API responses (User, Repository, FileNode, etc.)
- Set up axios client with baseURL and credential support
- Add response interceptor for 401 redirect handling
- Implement auth API functions (getCurrentUser, logout)
- Implement repos API functions (listRepositories, listFiles, getFileContent)
- Create React Query hooks for data fetching:
* useCurrentUser - fetch authenticated user
* useLogout - logout mutation
* useRepositories - fetch repos with sorting
* useFiles - fetch file tree with extension filtering
* useFileContent - fetch individual file content
- All hooks use proper query keys and enabled conditions