feat(runtime): 启动时扫描并接管已有窗口

从 handle_map_request 中提取 populate_window_event 供复用，
新增 backend_scan_windows 扫描 X11 根窗口子树，
runtime_scan 将扫描到的窗口走完整 policy 流程纳入管理。
route_map_request 增加 override_redirect 过滤。

src/backend/x11/backend.c

@@ -22,8 +22,10 @@
 #include "base/macros.h"
 #include "base/memory.h"
 #include "base/window_list.h"
+#include "core/event.h"
 #include "core/plan.h"
 #include "core/types.h"
+#include "core/window.h"
 #include "internal.h"
 
 typedef struct atom_item_t {
@@ -625,3 +627,54 @@ bool backend_apply_effect(
   xcb_flush(backend->conn);
   return true;
 }
+
+backend_scan_result_t *backend_scan_windows(backend_t *backend) {
+  auto conn   = backend->conn;
+  auto root   = backend->screen->root;
+  auto cookie = xcb_query_tree_unchecked(conn, root);
+  auto reply  = xcb_query_tree_reply(conn, cookie, nullptr);
+  if (!reply) return nullptr;
+
+  auto length = xcb_query_tree_children_length(reply);
+  if (!length) {
+    p_delete(&reply);
+    return nullptr;
+  }
+
+  auto list = xcb_query_tree_children(reply);
+
+  backend_scan_result_t *result = p_new(backend_scan_result_t, 1);
+
+  for (int i = 0; i < length; i++) {
+    auto slot = (window_map_request_event_t *)
+      array_push(result->windows, result->count, result->capacity);
+    if (!populate_window_event(backend, list[i], slot)) {
+      window_layer_props_cleanup(&slot->props);
+      window_metadata_cleanup(&slot->metadata);
+      result->count--;
+    }
+  }
+
+  p_delete(&reply);
+
+  if (result->count == 0) {
+    backend_scan_result_destroy(result);
+    result = nullptr;
+    return nullptr;
+  }
+
+  return result;
+}
+
+void backend_scan_result_destroy(backend_scan_result_t *result) {
+  if (!result) return;
+
+  for (size_t i = 0; i < result->count; i++) {
+    window_map_request_event_t *ev = &result->windows[i];
+    window_layer_props_cleanup(&ev->props);
+    window_metadata_cleanup(&ev->metadata);
+  }
+
+  p_delete(&result->windows);
+  p_delete(&result);
+}

src/backend/x11/event.c

@@ -91,18 +91,13 @@ static bool urgent_from_states(
   return false;
 }
 
-static bool handle_map_request(
+bool populate_window_event(
   backend_t *backend,
-  event_t *event,
-  const xcb_map_request_event_t *xcb_event
+  xcb_window_t window,
+  window_map_request_event_t *ev
 ) {
-  xcb_window_t window = xcb_event->window;
-
-  event->type = ZDWM_EVENT_WINDOW_MAP_REQUEST;
-
-  window_map_request_event_t *ev = &event->as.window_map_request;
-  ev->window                     = (window_id_t)window;
-  ev->transient_for              = window_get_transient_for(backend, window);
+  ev->window        = (window_id_t)window;
+  ev->transient_for = window_get_transient_for(backend, window);
 
   xcb_get_window_attributes_reply_t *wa =
     window_get_attributes(backend, window);
@@ -167,6 +162,19 @@ static bool handle_map_request(
   return true;
 }
 
+static bool handle_map_request(
+  backend_t *backend,
+  event_t *event,
+  const xcb_map_request_event_t *xcb_event
+) {
+  event->type = ZDWM_EVENT_WINDOW_MAP_REQUEST;
+  return populate_window_event(
+    backend,
+    xcb_event->window,
+    &event->as.window_map_request
+  );
+}
+
 static bool handle_unmap_notify(
   backend_t *backend,
   event_t *event,

src/backend/x11/internal.h

@@ -7,6 +7,7 @@
 #include <xcb/xproto.h>
 
 #include "base/window_list.h"
+#include "core/event.h"
 
 #define ATOM_LIST(X)                   \
   X(COMPOUND_TEXT)                     \
@@ -94,3 +95,9 @@ struct backend_t {
   window_list_t map;
   window_list_t kill;
 };
+
+bool populate_window_event(
+  struct backend_t *backend,
+  xcb_window_t window,
+  window_map_request_event_t *ev
+);