feat(mobile-next): 导入官方 openim-flutter-demo 固定基线 3.8.3-patch.3 并完成双构建

- 上游: github.com/OpenIMSDK/openim-flutter-demo tag 3.8.3-patch.3
  commit b3dfdb1e8aaeaaf6f0793e10cadd20d5c184a31f
- 并行目录 mobile-next/ 原样导入（含 LICENSE），不覆盖现网 mobile/
- 锁定 Flutter 3.24.5 / Dart 3.5.4 / JDK 17 / Gradle 7.6.3 / AGP 7.3.1
- 实测 Android debug 与 release 构建均成功（见 docs/mobile-next-baseline-import.md）
- 本提交可单独回退：git revert 1db1229（重写前）

Co-authored-by: multica-agent <github@multica.ai>

mobile-next/openim_common/lib/src/urls.dart

@@ -0,0 +1,22 @@
+import 'config.dart';
+
+class Urls {
+  static final onlineStatus = "${Config.imApiUrl}/manager/get_users_online_status";
+  static final queryAllUsers = "${Config.imApiUrl}/manager/get_all_users_uid";
+  static final updateUserInfo = "${Config.appAuthUrl}/user/update";
+  static final searchFriendInfo = "${Config.appAuthUrl}/friend/search";
+  static final getUsersFullInfo = "${Config.appAuthUrl}/user/find/full";
+  static final searchUserFullInfo = "${Config.appAuthUrl}/user/search/full";
+
+  static final getVerificationCode = "${Config.appAuthUrl}/account/code/send";
+  static final checkVerificationCode = "${Config.appAuthUrl}/account/code/verify";
+  static final register = "${Config.appAuthUrl}/account/register";
+
+  static final resetPwd = "${Config.appAuthUrl}/account/password/reset";
+  static final changePwd = "${Config.appAuthUrl}/account/password/change";
+  static final login = "${Config.appAuthUrl}/account/login";
+
+  static final upgrade = "${Config.appAuthUrl}/app/check";
+  static final getClientConfig = '${Config.appAuthUrl}/client_config/get';
+  static final getTokenForRTC = "${Config.appAuthUrl}/user/rtc/get_token";
+}