fix: replace Worker thread with direct Bun.serve() for Windows compatibility

On Windows, Bun Worker threads with Bun.serve() accept TCP connections
but the fetch handler never fires, causing the web server to hang
indefinitely without sending any HTTP response.

This fix replaces the Worker-based architecture with direct Bun.serve()
in the main thread, which works reliably across all platforms.

Changes:
- web-server.ts: Use Bun.serve() directly instead of spawning a Worker
  thread. Import and inline request handling from api-handlers.
- web-server-worker.ts: Kept as-is for reference/future use.

Fixes the "Web UI connects but never responds" issue on Windows.

Author: kui123456789