refactor(chain): 处理链功能域 mixin 化，清理未使用导入并根治兼容层循环导入

- ChainBase 拆分为 RecognitionMixin/MessageProcessingMixin/NotificationMixin
- TransferChain 拆分为 7 个功能 mixin（_mixins.py），SubscribeChain 音乐订阅域拆出 _music.py
- 斜杠命令交互四件套收敛为 InteractionChainMixin 委托，会话管理器移至 application 层，chain 层不再 re-export
- 模块基础类收敛到 app/modules/_base（notification/mediaserver 语义重命名）
- 清理 app/chain/__init__.py 24 个未使用导入，修正 49 处测试 patch 目标到实际命名空间
- 兼容层 legacy 符号不再并入 __all__，根治 schemas 初始化反向拉起 application.transfer 的循环导入
- 修复 bangumi 集数为字符串时 set_bangumi_info 抛 TypeError
- 新增重复代码等架构门禁测试；capability 清单校验排除下划线内部目录

tests/test_manual_transfer_history.py

@@ -36,12 +36,12 @@ def _patch_transfer_planning(monkeypatch, chain, fileitem, history, planned, del
     monkeypatch.setattr(chain, "_TransferChain__put_to_jobview", lambda task: True)
     monkeypatch.setattr(
         chain,
-        "_TransferChain__register_scrape_batch_task",
+        "_register_scrape_batch_task",
         lambda task: None,
     )
     monkeypatch.setattr(
         chain,
-        "_TransferChain__close_scrape_batch",
+        "_close_scrape_batch",
         lambda batch_id: None,
     )
 
@@ -62,6 +62,7 @@ def _patch_transfer_planning(monkeypatch, chain, fileitem, history, planned, del
         "app.chain.transfer.TransferHistoryOper",
         lambda: history_oper,
     )
+    monkeypatch.setattr("app.chain._mixins.TransferHistoryOper", lambda: history_oper)
     monkeypatch.setattr(
         "app.chain.transfer.DownloadHistoryOper",
         lambda: SimpleNamespace(
@@ -71,10 +72,17 @@ def _patch_transfer_planning(monkeypatch, chain, fileitem, history, planned, del
             get_by_path=lambda path: None,
         ),
     )
+    monkeypatch.setattr("app.chain._mixins.DownloadHistoryOper", lambda: SimpleNamespace(
+            get_by_hash=lambda download_hash: None,
+            get_file_by_fullpath=lambda fullpath: None,
+            get_files_by_savepath=lambda savepath: [],
+            get_by_path=lambda path: None,
+        ))
     monkeypatch.setattr(
         "app.chain.transfer.SystemConfigOper",
         lambda: SimpleNamespace(get=lambda key: None),
     )
+    monkeypatch.setattr("app.chain._mixins.SystemConfigOper", lambda: SimpleNamespace(get=lambda key: None))
     monkeypatch.setattr(
         "app.chain.transfer.StorageChain",
         lambda: SimpleNamespace(
@@ -85,6 +93,13 @@ def _patch_transfer_planning(monkeypatch, chain, fileitem, history, planned, del
             or True,
         ),
     )
+    monkeypatch.setattr("app.chain._mixins.StorageChain", lambda: SimpleNamespace(
+            exists=lambda current_fileitem: True,
+            delete_media_file=lambda current_fileitem: deleted.append(
+                ("target", current_fileitem.path)
+            )
+            or True,
+        ))
     monkeypatch.setattr(
         "app.chain.transfer.MetaInfoPath",
         lambda path, custom_words=None, **kwargs: FakeMeta(1),