core: 明确布局函数返回语义与 floating 布局约定

src/core/runtime.h

@@ -0,0 +1,11 @@
+#include "core/state.h"
+
+typedef struct wm_runtime_t {
+  bool running;
+  bool will_restart;
+
+  wm_state_t state;
+} wm_runtime_t;
+
+bool wm_runtime_init(wm_runtime_t *runtime);
+void wm_runtime_shutdown(wm_runtime_t *runtime);