fix(canvas): 移动端侧边栏适配 — 抽屉式隐藏 + 汉堡菜单 + 全页面 scrim #89 (#90)

- app-top-nav.tsx: 移动端侧边栏默认 w-0（完全隐藏），展开时通过 is-mobile-expanded
  变为 absolute 浮层；scrim 移除 spatialWorkbench 条件，全页面通用；
  stage 区域添加 lg:hidden 汉堡菜单按钮切换侧边栏显隐
- globals.css: 移动端 @media 规则通用化，is-mobile-expanded 浮层行为从
  .is-spatial 限定改为 .app-workspace-shell 通用，scrim left 从 202px 改为 0

Co-authored-by: sikongyue <3155157671@qq.com>

web/src/styles/globals.css

@@ -599,10 +599,10 @@
 
     @media (max-width: 1023px) {
         .app-workspace-sidebar-scrim {
-            left: 202px;
+            left: 0;
         }
 
-        .app-workspace-shell.is-spatial .app-workspace-sidebar.is-mobile-expanded {
+        .app-workspace-shell .app-workspace-sidebar.is-mobile-expanded {
             position: absolute;
             z-index: 40;
             inset: 6px auto 6px 6px;