feat: align shared app foundations

lib/common/storage/storage_keys.dart

@@ -8,6 +8,11 @@ const storageJinzhiPurityPresets = 'jinzhi_purity_presets';
 const storageJinzhiPriceColorMode = 'jinzhi_price_color_mode';
 const storageJinzhiMockLoggedIn = 'jinzhi_mock_logged_in';
 
+// Previous builds could persist credentials in SharedPreferences. These keys
+// exist only for one-time migration into secure storage.
+const storageLegacyAccessToken = 'access_token';
+const storageAuthSessionActive = 'auth_session_active';
+
 // 设备/广告标识。由各自的 SDK/ATT 流程写入，DeviceHeaderService 读出注入
 // header；未写入则为空、注入时被过滤。
 const storageDeviceToken = 'device_token'; // 推送 token