fix: restore UI and fix scheduling logic
- Fixed React SPA UI: resolved hook ordering, stale closures in intervals, and incorrect dark mode CSS selectors
- Fixed scheduling logic: replaced cron with a loop to support immediate 'Run Now' triggers and dynamic Twitter config updates
- Added 'Clear Cache' feature to both backend and frontend for manual re-syncing
- Ensured Twitter client is properly re-initialized when cookies are updated via the web UI
- Fixed type errors and missing imports in the server and index files