feat(core): 引入 plan/effect 执行骨架

新增 plan/effect 数据结构与基础操作
在 runtime 中接入 event -> command_buffer -> plan -> backend 流程
补齐 policy/backend 接口并同步更新测试构建

src/core/policy.h

@@ -2,6 +2,7 @@
 
 #include "core/command_buffer.h"
 #include "core/event.h"
+#include "core/plan.h"
 #include "core/rules.h"
 #include "core/state.h"
 
@@ -12,3 +13,5 @@ typedef struct policy_context_t {
 } policy_context_t;
 
 bool policy_route_event(const policy_context_t *ctx, command_buffer_t *out);
+bool policy_apply_command(const policy_context_t *ctx,
+                          const command_buffer_t *command_buffer, plan_t *plan);