feat(web): 重构组件样式并添加确认对话框组件

- 优化组件视觉风格: 使用渐变色、阴影和圆角增强现代感
- 添加 ConfirmDialog 组件和 useConfirm hook 用于确认操作
- 改进聊天界面: 添加滚动到底部按钮、斜杠命令自动弹出
- 统一组件间距和颜色方案，提升 UI 一致性

web/client/src/index.css

@@ -4,30 +4,37 @@
 
 @layer base {
   * {
-    @apply border-zinc-200;
+    @apply border-zinc-200/60;
   }
   body {
-    @apply bg-white text-zinc-900;
+    @apply bg-white text-zinc-900 antialiased;
   }
-  /* Custom scrollbar */
+  /* Modern scrollbar */
   ::-webkit-scrollbar {
-    width: 6px;
-    height: 6px;
+    width: 5px;
+    height: 5px;
   }
   ::-webkit-scrollbar-track {
     background: transparent;
   }
   ::-webkit-scrollbar-thumb {
-    background: #d4d4d8;
-    border-radius: 3px;
+    background: rgba(161, 161, 170, 0.35);
+    border-radius: 10px;
   }
   ::-webkit-scrollbar-thumb:hover {
-    background: #a1a1aa;
+    background: rgba(161, 161, 170, 0.6);
   }
   /* Firefox scrollbar */
   * {
     scrollbar-width: thin;
-    scrollbar-color: #d4d4d8 transparent;
+    scrollbar-color: rgba(161, 161, 170, 0.35) transparent;
+  }
+}
+
+@layer utilities {
+  /* Skeleton shimmer animation */
+  .skeleton {
+    @apply bg-zinc-100 rounded-md animate-pulse;
   }
 }