chore(frontend): 新增全局 Toast 通知组件与入场动画

components/ui/Toast.tsx:
- Context + Provider 模式，全局可用 useToast() hook
- 支持 success / error / info 三种类型，颜色自动适配
- 3.5s 自动消失，支持手动关闭
- 固定右下角渲染，z-[9999]

index.css:
- 新增 @keyframes slide-in 右侧滑入动画

frontend/src/components/ui/Toast.tsx

@@ -0,0 +1,99 @@
+import {
+  createContext,
+  useContext,
+  useState,
+  useCallback,
+  type ReactNode,
+} from "react";
+import { X, CheckCircle, AlertCircle, Info } from "lucide-react";
+
+// ============================================================
+// 类型
+// ============================================================
+
+type ToastType = "success" | "error" | "info";
+
+interface ToastItem {
+  id: number;
+  message: string;
+  type: ToastType;
+}
+
+interface ToastContextValue {
+  toast: (message: string, type?: ToastType) => void;
+}
+
+// ============================================================
+// Context
+// ============================================================
+
+const ToastContext = createContext<ToastContextValue | null>(null);
+
+export function useToast() {
+  const ctx = useContext(ToastContext);
+  if (!ctx) throw new Error("useToast 必须在 ToastProvider 内使用");
+  return ctx;
+}
+
+// ============================================================
+// Provider
+// ============================================================
+
+let _nextId = 1;
+
+export function ToastProvider({ children }: { children: ReactNode }) {
+  const [items, setItems] = useState<ToastItem[]>([]);
+
+  const toast = useCallback((message: string, type: ToastType = "info") => {
+    const id = _nextId++;
+    setItems((prev) => [...prev, { id, message, type }]);
+    setTimeout(() => {
+      setItems((prev) => prev.filter((t) => t.id !== id));
+    }, 3500);
+  }, []);
+
+  return (
+    <ToastContext.Provider value={{ toast }}>
+      {children}
+
+      {/* Toast 渲染区 */}
+      <div className="fixed bottom-6 right-6 z-[9999] flex flex-col-reverse gap-2">
+        {items.map((item) => {
+          const icon =
+            item.type === "success" ? (
+              <CheckCircle className="h-4 w-4 text-green-500" />
+            ) : item.type === "error" ? (
+              <AlertCircle className="h-4 w-4 text-red-500" />
+            ) : (
+              <Info className="h-4 w-4 text-blue-500" />
+            );
+
+          const borderColor =
+            item.type === "success"
+              ? "border-green-200 bg-green-50"
+              : item.type === "error"
+                ? "border-red-200 bg-red-50"
+                : "border-blue-200 bg-blue-50";
+
+          return (
+            <div
+              key={item.id}
+              className={`flex items-center gap-2 rounded-lg border px-4 py-3 shadow-lg animate-slide-in ${borderColor} min-w-[280px] max-w-sm`}
+            >
+              {icon}
+              <span className="flex-1 text-sm text-gray-700">{item.message}</span>
+              <button
+                onClick={() =>
+                  setItems((prev) => prev.filter((t) => t.id !== item.id))
+                }
+                className="text-gray-400 hover:text-gray-600"
+              >
+                <X className="h-3.5 w-3.5" />
+              </button>
+            </div>
+          );
+        })}
+      </div>
+    </ToastContext.Provider>
+  );
+}

frontend/src/index.css

@@ -34,3 +34,22 @@ body {
   width: 0;
   height: 0;
 }
+
+/* ============================================================
+   Toast 动画
+   ============================================================ */
+
+@keyframes slide-in {
+  from {
+    opacity: 0;
+    transform: translateX(100%);
+  }
+  to {
+    opacity: 1;
+    transform: translateX(0);
+  }
+}
+
+.animate-slide-in {
+  animation: slide-in 0.3s ease-out;
+}