fix(login): translated error messages for failed and rate-limited logins

Map INVALID_CREDENTIALS and TOO_MANY_ATTEMPTS to i18n keys. A non-JSON error body (Traefik 502/504) no longer shows as a network error.

src/pages/LoginPage.jsx

@@ -10,6 +10,11 @@ import AuthLayout from '../components/AuthLayout.jsx';
 import FeedbackAlert from '../components/FeedbackAlert.jsx';
 import {getValidToken} from '../utils/auth.js';
 
+const LOGIN_ERROR_KEY = {
+    INVALID_CREDENTIALS: 'LOGIN.ERROR_INVALID_CREDENTIALS',
+    TOO_MANY_ATTEMPTS: 'LOGIN.ERROR_TOO_MANY_ATTEMPTS',
+};
+
 export default function LoginPage() {
     const {t} = useTranslation();
     const navigate = useNavigate();
@@ -40,17 +45,16 @@ export default function LoginPage() {
                 body: JSON.stringify({email, password}),
             });
 
-            // Parse the JSON response (matches our Spring Boot LoginResponse record)
-            const data = await response.json();
+            // A proxy error (502/504) has an HTML body, so a parse failure is not a network error.
+            const data = await response.json().catch(() => ({}));
 
             if (response.ok) {
-                // HTTP 200 OK
                 localStorage.setItem('tbp_jwt', data.token);
                 navigate('/dashboard', {replace: true});
             } else {
-                // HTTP 401 Unauthorized or other errors
+                const minutes = Math.ceil(Number(response.headers.get('Retry-After') ?? 900) / 60);
                 setFeedback({
-                    message: `Error: ${data.message || 'Login failed'}`,
+                    message: t(LOGIN_ERROR_KEY[data.code] ?? 'LOGIN.ERROR_GENERIC', {minutes}),
                     isError: true
                 });
             }
@@ -58,7 +62,7 @@ export default function LoginPage() {
             // Network errors (e.g., backend is not running or CORS issue)
             console.error('Login API Error:', error);
             setFeedback({
-                message: 'Network error: Could not connect to the authentication service.',
+                message: t('INFO.ERROR.NETWORK_FAILURE'),
                 isError: true
             });
         } finally {