refactor(chain): chain 与 module 仅经 run_module 契约互联，实现模块内容封闭

- mTorrent 字幕链接解析下沉为 IndexerModule.site_subtitle_links，subtitle 模块自行跳过 API 站点
- TMDB/MusicBrainz 识别缓存管理改为模块方法（tmdb_cache_*/music_cache_*）经 run_module 分发
- WechatClawBot 客户端查找/临时客户端/缓存迁移内聚为 wechatclawbot_* 模块方法，
  chain 移除 WechatClawBot 类与 ModuleManager 内省
- LISTENBRAINZ_* 常量迁至 schemas/types.py，模块与链层再导入保持兼容
- TMDbException 升为 schemas/exception.py 跨层契约，vendored 异常保持类身份一致
- 架构守护测试新增 test_chain_does_not_import_module_internals（共 18 项）
- 文档同步：chain->module 仅允许 run_module 分发，直接导入禁止

AGENTS.md

@@ -69,7 +69,7 @@ The legacy roots have no physical directories in the source tree. Current images
 | `app/application/` | 读取配置/持久化状态的聚焦应用服务和服务族规则 | 多领域 Chain 编排、底层通用机制、通用传输协议 | `recognition.py`, `filter.py`, `filter_rules.py`, `notification.py`, `mediaserver.py`, `rss.py`, `site/sites.*` |
 | `app/application/messaging/` | 消息渲染/路由、交互和 Agent 到消息桥接：`interaction.py` 通用交互契约和视图工具；`router.py` 统一交互优先级和回调分发；`site.py`/`subscribe.py`/`skill.py` 对应命令的会话、输入解析和视图；`media.py` 媒体交互状态（业务工作流仍由 `MediaInteractionChain` 执行）；`plugin.py` 插件输入接管和插件按钮回调；`agent.py` Agent 选择状态、回调协议和 WebAgent 消息桥接；`message.py` 通知渲染、模板和队列。不作为推荐给插件直接使用的公开 SDK | 认证策略、通用 HTTP、服务发现、仅端点使用的 Web Push 行为 | `message.py`, `interaction.py`, `router.py`, `agent.py` |
 | `app/application/security/` | 认证、授权、Cookie、Passkey、OTP/二次认证、路径/URL 安全、SSRF 和签名策略 | 通用 URL 解析、进程运行策略、普通业务校验 | `access.py`, `auth.py`, `cookie.py`, `passkey.py`, `otp.py`, `twofactor.py`, `url.py` |
-| `app/chain/` | Reusable use-case orchestration across modules, services, Oper classes, events, and caches | Transport schemas, backend-specific protocol details, generic primitives | `media.py`, `download.py`, `subscribe.py`, `transfer.py` |
+| `app/chain/` | Reusable use-case orchestration across modules, services, Oper classes, events, and caches; chains reach modules only through `run_module` dispatch on method-name contracts | Transport schemas, backend-specific protocol details, generic primitives, direct imports of module internals (classes, exceptions, constants) | `media.py`, `download.py`, `subscribe.py`, `transfer.py` |
 | `app/startup/` | Composition root: inject providers/adapters, order initialization and shutdown, decide restart/lifecycle policy | Reusable business rules or adapter implementation details | `lifecycle.py`, `domain_initializer.py`, `cache_initializer.py`, `modules_initializer.py` |
 | `app/sdk/` | Deliberately curated stable imports for new plugins | Canonical implementation logic or host-internal dependencies | `cache.py`, `logging.py`, `media.py`, `network.py`, `services.py` |
 | `app/runtime/compat/` | 仅依赖标准库的精确旧导入路由和 DEBUG 诊断 | 业务实现、通配猜测、目标模块的提前导入 | `manifest.py`, `imports.py`, `diagnostics.py` |