feat: initial frontend - React + TypeScript + Vite

- Login page with JWT auth
- Dashboard with stats and charts
- Issues list with pagination, filtering
- Issue detail with comments, status transitions
- Create issue form
- Dark theme UI
- Docker (nginx) with API proxy to backend
- Sidebar navigation

src/App.tsx

@@ -0,0 +1,39 @@
+import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom'
+import { useAuth } from '@/hooks/useAuth'
+import Sidebar from '@/components/Sidebar'
+import LoginPage from '@/pages/LoginPage'
+import DashboardPage from '@/pages/DashboardPage'
+import IssuesPage from '@/pages/IssuesPage'
+import IssueDetailPage from '@/pages/IssueDetailPage'
+import CreateIssuePage from '@/pages/CreateIssuePage'
+
+export default function App() {
+  const { user, loading, login, logout } = useAuth()
+
+  if (loading) return <div className="loading">加载中...</div>
+
+  if (!user) {
+    return (
+      <BrowserRouter>
+        <LoginPage onLogin={login} />
+      </BrowserRouter>
+    )
+  }
+
+  return (
+    <BrowserRouter>
+      <div className="app-layout">
+        <Sidebar user={user} onLogout={logout} />
+        <main className="main-content">
+          <Routes>
+            <Route path="/" element={<DashboardPage />} />
+            <Route path="/issues" element={<IssuesPage />} />
+            <Route path="/issues/new" element={<CreateIssuePage />} />
+            <Route path="/issues/:id" element={<IssueDetailPage />} />
+            <Route path="*" element={<Navigate to="/" />} />
+          </Routes>
+        </main>
+      </div>
+    </BrowserRouter>
+  )
+}