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/data.json

@@ -0,0 +1,52 @@
+{
+  errCode: 0,
+  errMsg: "",
+  data: {
+    userFullInfoList: [
+      {
+        userID: "2380124277",
+        password: "",
+        account: "11002",
+        phoneNumber: "",
+        areaCode: "",
+        nickname: "林玟书",
+        englishName: "",
+        faceURL: "",
+        gender: 1,
+        mobileAreaCode: "+86",
+        mobile: "",
+        telephone: "",
+        level: 1,
+        birth: 288316800000,
+        email: "",
+        order: 0,
+        status: 0,
+        allowAddFriend: 1,
+        allowBeep: 1,
+        allowVibration: 1,
+        forbidden: 0,
+        station: "",
+        departmentList: [
+          {
+            departmentID: "936609157",
+            departmentFaceURL: "",
+            departmentName: "前端",
+            departmentParentID: "1852915335",
+            departmentOrder: 0,
+            departmentDepartmentType: 0,
+            departmentRelatedGroupID: "",
+            departmentCreateTime: 1678095053014,
+            memberOrder: 0,
+            memberPosition: "IOS",
+            memberLeader: 0,
+            memberStatus: 0,
+            memberEntryTime: 0,
+            memberTerminationTime: 0,
+            memberCreateTime: 1678095467228
+          }
+        ]
+      }
+    ],
+    totalNumber: 1
+  }
+}