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/pages/LoginPage.tsx

@@ -0,0 +1,54 @@
+import React, { useState } from 'react'
+
+interface Props {
+  onLogin: (username: string, password: string) => Promise<void>
+}
+
+export default function LoginPage({ onLogin }: Props) {
+  const [username, setUsername] = useState('')
+  const [password, setPassword] = useState('')
+  const [error, setError] = useState('')
+  const [loading, setLoading] = useState(false)
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault()
+    setError('')
+    setLoading(true)
+    try {
+      await onLogin(username, password)
+    } catch {
+      setError('登录失败，请检查用户名和密码')
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  return (
+    <div className="login-page">
+      <div className="login-card">
+        <h1>⚓ HarborForge</h1>
+        <p className="subtitle">Agent/人类协同任务管理平台</p>
+        <form onSubmit={handleSubmit}>
+          <input
+            type="text"
+            placeholder="用户名"
+            value={username}
+            onChange={(e) => setUsername(e.target.value)}
+            required
+          />
+          <input
+            type="password"
+            placeholder="密码"
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+            required
+          />
+          {error && <p className="error">{error}</p>}
+          <button type="submit" disabled={loading}>
+            {loading ? '登录中...' : '登录'}
+          </button>
+        </form>
+      </div>
+    </div>
+  )
+}