feat(frontend): 实现任务全景树组件与三大操作弹窗

TaskTreeViewer (components/TaskTree/):
- 搜索栏: 输入 16 位序列号 → getTaskTree() → 递归渲染产品任务树
- 状态标签: PENDING(黄)/WIP(蓝)/COMPLETED(绿)/REJECTED(红)/ARCHIVED(灰)
- 返工警告: is_rework → 红色脉冲 ⚠返工 标签 + 红色 ring 边框
- 裂变标识: child_tasks>1 → 紫色 裂变×N 标签 + 树形连接线
- 产品摘要栏: 序列号/订单/当前位置(virtual_warehouse→🏭仓库)/任务总数

三大操作弹窗 (替换 alert 占位符):
- ReceiveConfirmModal: 二次确认 → receiveTask() → Toast + 刷新树
- RejectModal: 驳回原因必填(≤500字) → rejectTask() → 自动返工提示
- TransferModal: 工序名称 + 多接收人标签输入(Enter添加/X删除)
  + 🏭虚拟入库勾选 + 备注 + 实时裂变预览 → transferTask()

路由接入:
- App.tsx: 包裹 ToastProvider, 新增 /admin/tasks 路由
- AdminLayout: 侧边栏新增「任务全景」菜单 (GitBranch 图标)
- AdminTasksPage: 薄封装层

frontend/src/App.tsx

@@ -1,5 +1,6 @@
 import { BrowserRouter, Routes, Route, Navigate } from "react-router-dom";
 
+import { ToastProvider } from "./components/ui/Toast";
 import AppLayout from "./components/layout/AppLayout";
 import ScanPage from "./pages/ScanPage";
 import MyTasksPage from "./pages/MyTasksPage";
@@ -9,27 +10,31 @@ import ProfilePage from "./pages/ProfilePage";
 import AdminLayout from "./components/layout/AdminLayout";
 import AdminDashboard from "./pages/admin/AdminDashboard";
 import AdminProductsPage from "./pages/admin/AdminProductsPage";
+import AdminTasksPage from "./pages/admin/AdminTasksPage";
 
 export default function App() {
   return (
-    <BrowserRouter>
-      <Routes>
-        {/* 移动端 */}
-        <Route path="/" element={<Navigate to="/scan" replace />} />
-        <Route element={<AppLayout />}>
-          <Route path="/scan" element={<ScanPage />} />
-          <Route path="/tasks" element={<MyTasksPage />} />
-          <Route path="/notifications" element={<NotificationsPage />} />
-          <Route path="/profile" element={<ProfilePage />} />
-        </Route>
+    <ToastProvider>
+      <BrowserRouter>
+        <Routes>
+          {/* 移动端 */}
+          <Route path="/" element={<Navigate to="/scan" replace />} />
+          <Route element={<AppLayout />}>
+            <Route path="/scan" element={<ScanPage />} />
+            <Route path="/tasks" element={<MyTasksPage />} />
+            <Route path="/notifications" element={<NotificationsPage />} />
+            <Route path="/profile" element={<ProfilePage />} />
+          </Route>
 
-        {/* PC 管理端 */}
-        <Route path="/admin" element={<Navigate to="/admin/dashboard" replace />} />
-        <Route element={<AdminLayout />}>
-          <Route path="/admin/dashboard" element={<AdminDashboard />} />
-          <Route path="/admin/products" element={<AdminProductsPage />} />
-        </Route>
-      </Routes>
-    </BrowserRouter>
+          {/* PC 管理端 */}
+          <Route path="/admin" element={<Navigate to="/admin/dashboard" replace />} />
+          <Route element={<AdminLayout />}>
+            <Route path="/admin/dashboard" element={<AdminDashboard />} />
+            <Route path="/admin/products" element={<AdminProductsPage />} />
+            <Route path="/admin/tasks" element={<AdminTasksPage />} />
+          </Route>
+        </Routes>
+      </BrowserRouter>
+    </ToastProvider>
   );
 }