fix(explorer): 窗口创建/销毁时整体置脏，避免内容残留

抽出 mark_all_windows()（所有可见窗口整体置脏，含阴影带），CREATE 与 DESTROY 分支各调用一次并保留 mark_titles()。原来这两处只标记标题栏 + 任务栏：新建窗口的内容区不脏（可能空白），关窗后下方露出的旧内容也不会重画，都要等鼠标经过才恢复。focus() 的内联循环同步收敛到该函数。

Apps/Explorer/desk_server.vp

@@ -238,6 +238,13 @@ class DeskServer:
         if y + h + SHADOW_BOTTOM > tb:
             self.mark(tb, TASKBAR_H)
 
+    # 窗口集合/层级变化：所有可见窗口整体置脏（含阴影带）
+    def mark_all_windows(self):
+        for i in range(desk.DESK_MAX_WIN):
+            w: desk.WinSlot* = self.slot(i)
+            if w.used != 0 and w.active != 0 and w.minimized == 0:
+                self.mark_win(w.uy, w.h)
+
     # 活动窗口切换会改变标题栏配色：把所有窗口的标题栏行置脏
     def mark_titles(self):
         for i in range(desk.DESK_MAX_WIN):
@@ -1085,6 +1092,7 @@ class DeskServer:
             if nw >= 0:
                 ns: desk.WinSlot* = self.slot(nw)
                 string.memcpy(&ns.title, &m.title, uint64(desk.DESK_TITLE_MAX))
+            self.mark_all_windows()
             self.mark_titles()
             self.push_event_pid(m.pid, nw, uint32(desk.DESK_EVT_CREATED), nw, 0, 0, 0)
             return
@@ -1097,6 +1105,7 @@ class DeskServer:
             self.mark(s.uy, s.h)
             s.used = 0
             if self.focused == win: self.focused = -1
+            self.mark_all_windows()
             self.mark_titles()
         elif ty == uint32(desk.DESK_REQ_MOVE):
             self.mark_win(s.uy, s.h)
@@ -1150,12 +1159,8 @@ class DeskServer:
         self.next_z += 1
         s.z_order = self.next_z
         self.focused = win
-        # 层级变化会改变窗口互相覆盖的关系：把所有可见窗口整体置脏重画，
-        # 否则被抬起的窗口只重画标题栏，内容区仍露出原来压在上面的窗口，直到鼠标经过。
-        for i in range(desk.DESK_MAX_WIN):
-            w: desk.WinSlot* = self.slot(i)
-            if w.used != 0 and w.active != 0 and w.minimized == 0:
-                self.mark_win(w.uy, w.h)
+        # 层级变化会改变互相覆盖的关系：所有可见窗口整体置脏
+        self.mark_all_windows()
         self.mark_titles()
 
     def _move_cursor(self, dx: int, dy: int) -> int: