refactor(client): 网络层由官方 http 换成 dio（对外行为不变）

为什么：权威文档（AGENTS.md / CODING_STANDARDS.md）强制网络层用 dio，差异清单 A 组第 1 题
用户裁定选 A；原来用官方 http 是在无文档状态下按口头要求选的。

- ApiClient 改用 dio + BaseOptions（validateStatus 恒真、8s 超时、ResponseType.bytes 自行 UTF-8 解码）
- 新增 AuthHeaderInterceptor（Authorization / X-Device-Id）与 EnvelopeInterceptor
  （解包 {code,message,data} + 错误码映射 + 401 判定）
- 401 → 刷新 → 重发一次在 ApiClient 里编排，刻意不放在拦截器内重发：dio 的排队拦截器
  在回调里再发请求会自锁
- 接口层（auth_api/catalog_api）签名、全部 controller/logic/page 未改动
- 测试：新增假 dio adapter 替代 MockClient，断言口径一条未改；用例名改为 should_<期望>_when_<条件>；
  新增 api_client_test（解包/错误映射/请求头/查询参数/跳过重试）与 live_auth_test（真实后端 POST 链路）
- pubspec：加 dio、移除已无引用的 http
- 实测：dart analyze lib test 零告警；flutter test 155 全过；真实联调（8081）GET/POST 链路均通

pubspec.lock

@@ -89,6 +89,22 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.0.9"
+  dio:
+    dependency: "direct main"
+    description:
+      name: dio
+      sha256: "852ec3b48cc431ac04fff978413c541502b67ffc3e26921e74e3d994694192c1"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "5.11.1"
+  dio_web_adapter:
+    dependency: transitive
+    description:
+      name: dio_web_adapter
+      sha256: "3a1b2cd7be71086f38504956e3ebcd2837288d231ff454bafa78021244102bfc"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "2.2.2"
   fake_async:
     dependency: transitive
     description:
@@ -157,14 +173,6 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.15.7"
-  http:
-    dependency: "direct main"
-    description:
-      name: http
-      sha256: "87721a4a50b19c7f1d49001e51409bddc46303966ce89a65af4f4e6004896412"
-      url: "https://pub.flutter-io.cn"
-    source: hosted
-    version: "1.6.0"
   http_parser:
     dependency: transitive
     description:
@@ -253,6 +261,14 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.19.0"
+  mime:
+    dependency: transitive
+    description:
+      name: mime
+      sha256: bd47de35f07e27267e69c8c8b22edf9473bfee170a60d60fcc93730c5144b7f6
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "2.1.0"
   nested:
     dependency: transitive
     description: