feat(settings): add user-settings seam (ctx.settings) + file provider

Two-package capability family mirroring session-persistence/:

- dsh-settings: abstract Settings service — namespace registry with
  caller-fiber effect registrations, layered resolution (schema defaults
  < composition base < user document), schemastery validation,
  per-namespace deep-equal commit detection, and the settings/updated
  event. Boot/registration validation fails loud; provider publishes
  keep last-good per namespace.
- dsh-settings-local: settings.yaml/.json provider — resolveSpec
  defaulting to $DSH_HOME/settings.yaml, chokidar hot reload,
  content-equality self-write suppression, atomic 0600 tmp+rename
  writes, comment-preserving YAML namespace patching.

Consumers register inside ctx.inject(['settings'], …), so every
composition works unchanged without a mounted provider. Real Loader +
Include composition test proves cordis.yml boot and external-edit hot
propagation; HMR disposal test proves registry cleanup. Both packages
hold per-file 100% coverage.

Doc budgets rise 1705→1710 (AGENTS.md) and 835→845 (packages/README.md):
one structural line per file for the new package group.

Agent Note: .agents/notes/implemented/architecture/2026-07-28-user-settings-seam.md

docs/config-catalog.md

@@ -1177,6 +1177,24 @@ Depends on: [`SessionTitleLlmConfig`](../packages/session-title/session-title-ll
 
 Source: [`packages/session-title/session-title-first-message-llm/src/index.ts:15`](../packages/session-title/session-title-first-message-llm/src/index.ts)
 
+## `@deepseek-ai/dsh-settings-local`
+
+```ts config-catalog
+/** Plugin config: file location and hot-reload behavior. */
+export interface Config {
+  /** Settings document path; defaults to `settings.yaml` under the harness home. */
+  path?: string
+  /** Harness home used when `path` is omitted; defaults to `$DSH_HOME` or `~/.dsh`. */
+  dshHome?: string
+  /** Watch the document and hot-publish external edits; defaults to true. */
+  watch?: boolean
+  /** Watcher write-settle window in milliseconds; defaults to 100. */
+  debounceMs?: number
+}
+```
+
+Source: [`packages/settings/settings-local/src/index.ts:18`](../packages/settings/settings-local/src/index.ts)
+
 ## `@deepseek-ai/dsh-skill`
 
 ```ts config-catalog
@@ -2192,6 +2210,7 @@ Abstract service classes — a deployment loads a concrete implementation packag
 - `@deepseek-ai/dsh-sandbox` — abstract `SandboxProvider` ([`packages/sandbox/sandbox/src/index.ts`](../packages/sandbox/sandbox/src/index.ts))
 - `@deepseek-ai/dsh-session-persistence` — abstract `SessionPersistence` ([`packages/session-persistence/session-persistence/src/index.ts`](../packages/session-persistence/session-persistence/src/index.ts))
 - `@deepseek-ai/dsh-session-query` — abstract `SessionQueryService` ([`packages/session-query/session-query/src/index.ts`](../packages/session-query/session-query/src/index.ts))
+- `@deepseek-ai/dsh-settings` — abstract `Settings` ([`packages/settings/settings/src/index.ts`](../packages/settings/settings/src/index.ts))
 - `@deepseek-ai/dsh-spill` — abstract `SpillStore` ([`packages/spill/spill/src/index.ts`](../packages/spill/spill/src/index.ts))
 - `@deepseek-ai/dsh-subprocess` — abstract `SubprocessService` ([`packages/subprocess/subprocess/src/index.ts`](../packages/subprocess/subprocess/src/index.ts))
 - `@deepseek-ai/dsh-tasks` — abstract `TaskService` ([`packages/tasks/tasks/src/index.ts`](../packages/tasks/tasks/src/index.ts))