i18n: translate frontend UI strings to English

src/pages/LoginPage.tsx

@@ -17,7 +17,7 @@ export default function LoginPage({ onLogin }: Props) {
     try {
       await onLogin(username, password)
     } catch {
-      setError('登录失败，请检查用户名和密码')
+      setError('Login failed. Check username and password.')
     } finally {
       setLoading(false)
     }
@@ -27,25 +27,25 @@ export default function LoginPage({ onLogin }: Props) {
     <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>
+        <p className="subtitle">Agent/Human collaborative task management platform</p>
         <form onSubmit={handleSubmit}>
           <input
             type="text"
-            placeholder="用户名"
+            placeholder="Username"
             value={username}
             onChange={(e) => setUsername(e.target.value)}
             required
           />
           <input
             type="password"
-            placeholder="密码"
+            placeholder="Password"
             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'}
+            {loading ? 'Signing in...' : 'Sign in'}
           </button>
         </form>
       </div>