fix(HEL-240): 去掉登录页底部状态栏缺口

登录页覆盖全局 body 底边距，让左栏品牌面板铺满视口高度。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

tests/test_login_portal.py

@@ -40,6 +40,9 @@ class LoginPortalContractTests(unittest.TestCase):
         self.assertIn("width: var(--login-brand-share);", AUTH)
         self.assertIn("width: var(--login-card-width);", AUTH)
         self.assertIn("justify-content: flex-end;", AUTH)
+        self.assertIn("body.login-portal {", AUTH)
+        self.assertIn("padding-bottom: 0;", AUTH)
+        self.assertNotIn("padding: 0 0 var(--statusbar-height);", AUTH)
 
     def test_portal_keeps_account_switch_and_theme_hooks(self) -> None:
         self.assertIn("data-switch-id", LOGIN_JS)