feat: migrate serve WebSocket from ws crate to Axum

Migrates the live reload WebSocket server from the standalone `ws` crate
to native Axum WebSocket support:

- Replace ws::WebSocket with axum's built-in WebSocket extractor
- Use tokio::sync::broadcast for message broadcasting to clients
- Integrate WebSocket endpoint into main Axum router at /livereload
- Serve livereload.js via dedicated route instead of fallback handler
- Remove separate WebSocket server thread (now runs on same port as HTTP)

Also fixes build error notification via WebSocket:

- Send reload message on build errors so browser auto-refreshes
- Handle 404 responses in error_injection_middleware for error display
- Include livereload.js in error page so it can reload when fixed
- Don't interfere with WebSocket upgrades (101) in middleware

Additional improvements:

- Add WebSocket ping/pong keepalive (30s interval) for connection health
- Add graceful shutdown support via with_graceful_shutdown()
- Handle Message::Close and Message::Pong explicitly in WebSocket handler
- Remove unnecessary #[derive(Clone)] from AppState (already Arc-wrapped)

Cleanup of vestigial ws_port code:

- Remove ws_port parameter from create_new_site() function signature
- Simplify enable_live_reload_with_port() to use interface_port directly
- Update both call sites in serve() to remove the None argument
- Update test helper to remove ws_port parameter
- Fix test assertion to verify live_reload uses interface_port

Dependencies:

- Add "ws" feature to axum for WebSocket support
- Add "sync" feature to tokio for broadcast channels
- Remove ws, tower, tower-http, tracing, tracing-subscriber crates

Author: EvanCarroll