refactor(nav): 手机导航抽屉改用组件库 Drawer

- 删掉手写的抽屉（遮罩 / Esc / 标题 / 关闭按钮 / 动画）与对应 CSS
- 直接用 @stash/ui 的 Drawer（原生 dialog，自带焦点陷阱、Esc、backdrop 与滚动锁）
- 保留原来自定义的分组选择逻辑

stash-web/src/AppNext.tsx

@@ -1,16 +1,14 @@
 import {
   Breadcrumb,
   Card,
+  Drawer,
   Empty,
   EngineIcon,
-  Icon,
-  IconButton,
   Layout,
   Menu,
   Notice,
   SearchField,
   Space,
-  Title,
   Toaster,
   type EngineIconName,
   type MenuItem,
@@ -1042,29 +1040,15 @@ export default function AppNext() {
 
       <BackToTop visible={scrolled} targetId="page-scroll" />
 
-      {navOpen && (
-        <div className="nav-drawer">
-          <button
-            type="button"
-            className="nav-drawer-backdrop"
-            aria-label="关闭分组导航"
-            onClick={() => setNavOpen(false)}
-          />
-          <div className="nav-drawer-panel" role="dialog" aria-modal="true" aria-label="分组导航">
-            <div className="nav-drawer-head">
-              <Title level={4} as="h2" weight="semibold">
-                分组导航
-              </Title>
-              <IconButton
-                label="关闭分组导航"
-                icon={<Icon name="close_line" />}
-                onClick={() => setNavOpen(false)}
-              />
-            </div>
-            <Menu items={sidebarItems} activeKey={activeKey} itemHeight={44} onSelect={selectNav} />
-          </div>
-        </div>
-      )}
+      <Drawer
+        open={navOpen}
+        onClose={() => setNavOpen(false)}
+        title="分组导航"
+        placement="left"
+        width={300}
+      >
+        <Menu items={sidebarItems} activeKey={activeKey} itemHeight={44} onSelect={selectNav} />
+      </Drawer>
     </>
   )
 }