Fix concurrent connection issues in wsssht daemon mode

- Implement thread-based concurrent connection handling
- Fix segmentation fault caused by shared static variables
- Each connection now gets its own WebSocket tunnel and resources
- Replace global tunnel management with per-thread instances
- Add proper cleanup for individual connection threads
- Allow multiple SSH sessions to connect simultaneously to the same port

wssshtools/tunnel.h

@@ -66,6 +66,11 @@ int frame_buffer_resize(frame_buffer_t *fb, size_t new_size);
 int frame_buffer_append(frame_buffer_t *fb, const char *data, size_t len);
 int frame_buffer_consume(frame_buffer_t *fb, size_t len);
 
+// Helper functions for managing multiple tunnels
+tunnel_t *find_tunnel_by_request_id(const char *request_id);
+int add_tunnel(tunnel_t *tunnel);
+void remove_tunnel(const char *request_id);
+
 void *forward_tcp_to_ws(void *arg);
 void *forward_ws_to_local(void *arg);
 void *forward_ws_to_ssh_server(void *arg);