新增：媒体上传客户端——MediaUploader 编排状态机 + 预签名直传 + 进度组件，修正 media 端点误挂 community 服务（T3-13）

- MediaUploader：选图→压缩（80→60 降质阶梯，10 MiB 超限拒绝）→createUpload
  →预签名 PUT 直传（进度回调）→confirm→ready assetId 交付；并发槽位 2、
  顺序即 position、单图失败不拖垮整批；凭据过期预检与存储侧 403 各自动
  换新凭据一次；失败重试复用压缩产物、从 createUpload 全新开始
- 孤儿防护：未 confirm 的 assetId 只以管线局部变量存在，快照 assetId 与
  ready 态断言绑定，buildAttachRequests 非全员 ready 即抛 StateError
- 线路修正：media 两步上传端点由 user 服务（:8082 MediaController）提供,
  T3-12 误挂 community 客户端（:8084 无 media 路由），补 mediaApi 分端口
  直连，compose 真链路实测证实
- UploadProgressOverlay 四态进度层（05 号规范 §3.3）；直传层本地
  HttpServer 三线路测试（200/403/断连）；compose 冒烟测试
  （PATBOND_MEDIA_SMOKE=1 启用，默认跳过）
- 新依赖：image_picker、flutter_image_compress（03 号评估选型）
- flutter test 379 全绿（基线 347，+32）、analyze 0、format 无 diff

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/features/community/community_repository_test.dart

@@ -14,6 +14,7 @@ import '../../helpers/community_test_helpers.dart';
 void main() {
   late SessionManager session;
   late FakeHttpAdapter adapter;
+  late FakeHttpAdapter mediaAdapter;
   late ApiCommunityRepository repository;
 
   Future<void> setUpWith(
@@ -28,39 +29,58 @@ void main() {
     adapter = FakeHttpAdapter(handler);
     dio.httpClientAdapter = adapter;
     final refresher = TokenRefresher(dio: dio, session: session);
+    // media 两步上传端点由 user 服务提供（13 号报告 §2），走独立客户端;
+    // 两 adapter 分开记录以断言线路不串。
+    final mediaDio = buildPatbondDio(
+      session: session,
+      baseUrl: 'http://user.local',
+    );
+    mediaAdapter = FakeHttpAdapter(handler);
+    mediaDio.httpClientAdapter = mediaAdapter;
     repository = ApiCommunityRepository(
       api: ApiClient(dio: dio, session: session, refresher: refresher),
+      mediaApi: ApiClient(
+        dio: mediaDio,
+        session: session,
+        refresher: refresher,
+      ),
     );
   }
 
   group('请求线路（路径 / 方法 / 鉴权 / 参数）', () {
-    test('createMediaUpload：POST /api/v1/media/uploads，携带 Bearer', () async {
-      await setUpWith(
-        (options) async =>
-            jsonResponse(201, okEnvelope(sampleUploadCredentialsJson())),
-      );
+    test(
+      'createMediaUpload：POST /api/v1/media/uploads 走 user 服务客户端，携带 Bearer',
+      () async {
+        await setUpWith(
+          (options) async =>
+              jsonResponse(201, okEnvelope(sampleUploadCredentialsJson())),
+        );
 
-      final credentials = await repository.createMediaUpload(
-        const CreateMediaUploadRequest(
-          kind: MediaKind.image,
-          purpose: MediaPurpose.postImage,
-          mimeType: 'image/jpeg',
-          byteSize: 204800,
-        ),
-      );
+        final credentials = await repository.createMediaUpload(
+          const CreateMediaUploadRequest(
+            kind: MediaKind.image,
+            purpose: MediaPurpose.postImage,
+            mimeType: 'image/jpeg',
+            byteSize: 204800,
+          ),
+        );
 
-      final request = adapter.requests.single;
-      expect(request.path, '/api/v1/media/uploads');
-      expect(request.method, 'POST');
-      expect(request.headers['Authorization'], 'Bearer community-access');
-      expect(request.data, {
-        'kind': 'image',
-        'purpose': 'post_image',
-        'mimeType': 'image/jpeg',
-        'byteSize': 204800,
-      });
-      expect(credentials.uploadUrl, contains('X-Amz-Signature'));
-    });
+        // 线路：media 端点不打 community 客户端。
+        expect(adapter.requests, isEmpty);
+        final request = mediaAdapter.requests.single;
+        expect(request.baseUrl, 'http://user.local');
+        expect(request.path, '/api/v1/media/uploads');
+        expect(request.method, 'POST');
+        expect(request.headers['Authorization'], 'Bearer community-access');
+        expect(request.data, {
+          'kind': 'image',
+          'purpose': 'post_image',
+          'mimeType': 'image/jpeg',
+          'byteSize': 204800,
+        });
+        expect(credentials.uploadUrl, contains('X-Amz-Signature'));
+      },
+    );
 
     test('completeMediaUpload：POST /complete 无请求体（服务端幂等）', () async {
       await setUpWith(
@@ -70,7 +90,8 @@ void main() {
 
       final asset = await repository.completeMediaUpload('a-1');
 
-      final request = adapter.requests.single;
+      expect(adapter.requests, isEmpty);
+      final request = mediaAdapter.requests.single;
       expect(request.path, '/api/v1/media/uploads/a-1/complete');
       expect(request.method, 'POST');
       expect(asset.status, MediaAssetStatus.ready);