refactor: 从 core 中抽出跨模块契约建立 interface/common 模块分层

引入 interface/（零实现声明层）与 common/（共享 ADT 操作层），把跨模块
契约从 core 实现里抽出来，依赖方向回到单向（base ← interface ← common ←
各实现层）。docs/module-layering.org 记录完整方案与判定标准。

interface/（纯类型与多态接口声明，零 .c）：
- types.h / event.h / backend.h 从 core 移入
- effect.h 新建（effect_t 从 plan.h 抽出）

common/（多实现层共用的自包含操作，.h + .c）：
- event.{h,c}：event_reset / event_cleanup
- listeners.{h,c}：listeners 维护（add / cleanup）；notify 留 core
- window.{h,c}：window_list + layer_props/metadata cleanup + window_classify_layer
- workspace.{h,c}：workspace_desc（从 wm_desc.h 拆出，改真实函数）

window 相关整理：
- window_layer_type_t 上浮 interface/types.h（common 的 classify 需要）
- window_classify_layer 移 common/window
- window_info_t 独立成 core/window_info.h（state/command 共享，不寄生）
- 删除 wm_desc.h，base/window_list 并入 common/window

全项目 include 路径同步更新

src/core/plan.h

@@ -1,89 +1,10 @@
 #pragma once
 
 #include <stddef.h>
-#include <stdint.h>
 
 #include "base/color.h"
-#include "core/types.h"
-
-typedef enum effect_type_t {
-  ZDWM_EFFECT_MAP_WINDOW = 1,
-  ZDWM_EFFECT_UNMAP_WINDOW,
-  ZDWM_EFFECT_FOCUS_WINDOW,
-  ZDWM_EFFECT_KILL_WINDOW,
-  ZDWM_EFFECT_WITHDRAW_WINDOW,
-  ZDWM_EFFECT_START_MOVE_WINDOW,
-  ZDWM_EFFECT_START_RESIZE_WINDOW,
-  ZDWM_EFFECT_MINIMIZE_WINDOW,
-  ZDWM_EFFECT_MAXIMIZE_WINDOW,
-  ZDWM_EFFECT_FULLSCREEN_WINDOW,
-  ZDWM_EFFECT_CONFIGURE_WINDOW,
-  ZDWM_EFFECT_CHANGE_BORDER_COLOR,
-  ZDWM_EFFECT_CHANGE_WINDOW_LIST,
-  ZDWM_EFFECT_RESTACK_WINDOWS,
-  ZDWM_EFFECT_BIND_KEY,
-  ZDWM_EFFECT_GRAB_BUTTON,
-  ZDWM_EFFECT_UNGRAB_POINTER,
-} effect_type_t;
-
-typedef struct effect_move_window_t {
-  window_id_t window;
-  point_t left_top_point;
-} effect_move_window_t;
-
-typedef struct effect_resize_window_t {
-  window_id_t window;
-  int32_t width;
-  int32_t height;
-} effect_resize_window_t;
-
-typedef struct effect_change_border_color_t {
-  window_id_t window;
-  const color_t *color;
-} effect_change_border_color_t;
-
-typedef struct effect_window_list_t {
-  const window_id_t *windows;
-  size_t count;
-} effect_window_list_t;
-
-typedef struct effect_bind_key_t {
-  const key_bind_t *keys;
-  size_t count;
-} effect_bind_key_t;
-
-typedef struct effect_grab_button_t {
-  window_id_t window;
-  const grab_button_t *buttons;
-  size_t count;
-} effect_grab_button_t;
-
-typedef struct effect_bool_window_t {
-  window_id_t window;
-  bool value;
-} effect_bool_window_t;
-
-typedef struct effect_t {
-  effect_type_t type;
-  union {
-    only_window_data_t map;
-    only_window_data_t unmap;
-    only_window_data_t focus;
-    only_window_data_t kill;
-    only_window_data_t withdraw;
-    only_window_data_t move;
-    only_window_data_t resize;
-    effect_bool_window_t minimize;
-    effect_bool_window_t maximize;
-    effect_bool_window_t fullscreen;
-    configure_data_t configure;
-    effect_change_border_color_t change_border_color;
-    effect_window_list_t change_window_list;
-    effect_window_list_t restack_windows;
-    effect_bind_key_t bind_key;
-    effect_grab_button_t grab_button;
-  } as;
-} effect_t;
+#include "interface/effect.h"
+#include "interface/types.h"
 
 typedef struct plan_t {
   effect_t *effects;