feat(bar): 实现 bar 可见性切换 action

src/bar/bar.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <cairo.h>
 #include <stddef.h>
 #include <zdwm/bar.h>
 #include <zdwm/types.h>
@@ -7,6 +8,7 @@
 #include "bar/types.h"
 
 typedef struct bar_output_t {
+  cairo_t *cr;
   zdwm_window_id_t window_id;
   zdwm_output_id_t output_id;
   bar_side_t sides[ZDWM_BAR_SIDE_COUNT];