refactor(web): 工作区布局 - 顶部工具条融入主卡片背景

- 移除工具条独立圆角容器（边框/圆角/阴影/margin/独立底色），顶栏成为主区卡片背景的一部分，仅保留 44px 紧凑高度与内容区对齐

web/src/styles/globals.css

@@ -1335,23 +1335,14 @@
         position: relative;
         z-index: var(--z-toolbar);
         height: 44px;
-        margin: 8px 10px;
-        border: 1px solid color-mix(in srgb, var(--foreground) 5%, transparent);
-        border-radius: var(--r-lg);
-        background: var(--workspace-surface-strong);
-        box-shadow:
-            0 6px 18px color-mix(in srgb, var(--foreground) 6%, transparent),
-            inset 0 1px 0 color-mix(in srgb, white 6%, transparent);
+        border: 0;
+        border-radius: 0;
+        background: transparent;
+        box-shadow: none;
         backdrop-filter: none;
         -webkit-backdrop-filter: none;
     }
 
-    .dark .app-workspace-topbar {
-        box-shadow:
-            0 6px 18px rgba(0, 0, 0, 0.4),
-            inset 0 1px 0 color-mix(in srgb, white 6%, transparent);
-    }
-
     .app-workspace-topbar-icon-button {
         display: inline-flex;
         width: 36px;