Fix connect accumulation; add display sinks to enum-devices

- controller_cli: drain semaphore and reset pending_cmd in do_connect
  so stale posts from old connection don't unblock the next command
- protocol: add Proto_Display_Device_Info; extend
  proto_write_enum_devices_response and proto_read_enum_devices_response
  with display section; backward-compatible (absent in older messages)
- node: handle_enum_devices snapshots active Display_Slots under mutex
  and includes them in the response
- controller_cli: on_display callback prints display window info in
  enum-devices output
- query_cli: updated to pass NULL on_display (no display interest)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dev/cli/query_cli.c

@@ -195,7 +195,7 @@ static void on_frame(struct Transport_Conn *conn,
 			struct Proto_Response_Header hdr;
 			struct App_Error e = proto_read_enum_devices_response(
 				frame->payload, frame->payload_length, &hdr,
-				on_media_device, on_video_node, on_standalone, NULL);
+				on_media_device, on_video_node, on_standalone, NULL, NULL);
 			if (!APP_IS_OK(e)) { app_error_print(&e); }
 			else if (hdr.status != PROTO_STATUS_OK) {
 				fprintf(stderr, "ENUM_DEVICES failed: status=%u\n", hdr.status);