feat: 添加壁纸功能

src/wm.h

@@ -8,6 +8,7 @@
 #include "base.h"
 #include "status.h"
 #include "types.h"
+#include "wallpaper.h"
 
 typedef struct wm_t {
   padding_t padding;
@@ -49,6 +50,8 @@ typedef struct wm_t {
   struct xkb_context *xkb_ctx;
   struct xkb_state *xkb_state;
 
+  wallpaper_context_t *wallpaper;
+
   color_set_t color_set;
 } wm_t;