fix(llm,settings): refuse post-disposal route replacement and teardown notifications

Two lifecycle holes the registry and the consumer helper left open.

`AdapterRegistrationHandle.replace` had no liveness guard: after the handle's
disposer ran, a replace put routes back into the registry with nothing left to
release them, so the adapter leaked permanently. `owned` being empty cannot
carry that fact, because `replace([])` is the legal empty-section state, so the
disposer records it explicitly.

`installSettingsSection`'s watcher lacked the guard its own disposer carries:
a stored change landing while the consumer unloads reached `onChange`, which
re-registers routes against a fiber whose resources are being released.

Also documents `withFileLock` in the atomic-write README (it claimed one
export), records the age-based lock takeover as a known limitation, and lists
ctx.settings and ctx.credentials in the architecture capability table.

docs/architecture.zh.md

@@ -46,6 +46,8 @@
 | `ctx.sessionPersistence` | [`session-persistence/`](../packages/session-persistence/README.md) | 会话日志的持久化存储 |
 | `ctx.sessionQuery` | [`session-query/`](../packages/session-query/README.md) | 基于 SQLite 全文搜索的实时优先精确检索／过滤／追踪、经工作区授权的模型工具 |
 | `ctx.sessionTitle` | [`session-title/`](../packages/session-title/README.md) | 基于日志的回退标题和单个可选异步提供方 |
+| `ctx.settings` | [`settings/`](../packages/settings/README.md) | 按插件划分的用户设置命名空间，分层叠加在装配条目之上 |
+| `ctx.credentials` | [`credentials/`](../packages/credentials/README.md) | 具名密钥引用，按操作解析，绝不内联进配置 |
 | `ctx.directoryPicker` | [`host/directory-picker`](../packages/host/directory-picker/README.md) | GUI 宿主目录选取（`native`／`browse` 交互） |
 | `ctx.typert` | [`typert/registry`](../packages/typert/registry/README.md) | 生成的包反射和实时 Zod schema 的运行时注册表 |
 | `ctx.invariants` | [`support/invariants`](../packages/support/invariants/README.md) | 按包名筛选包自有运行时检查的注册表 |