feat(settings): detect stale writers with a revision, and announce raw changes

The remaining P1 from the #939 review, plus the P2 it shares a mechanism with.

Nothing carried a version, so two tabs editing one namespace silently
overwrote each other — reproduced as tab B's `reasoning` lost to tab A's
older draft. The seam's per-namespace write queue orders writes; it cannot
tell a fresh writer from one replaying a snapshot a predecessor superseded.

Each namespace now carries a monotonic `revision` over its RAW section. A
write may send `expectedRevision`, checked at the FRONT of the queue (not at
call time, which would race the very predecessor it guards against); a
mismatch rejects with `SettingsConflictError` → `settings-conflict` on the
wire, carrying both revisions. The editor captures the revision it opened at
and, on conflict, asks the user to reopen rather than replaying its snapshot.

The same counter fixes the missing broadcast. `settings/updated` is gated on
the resolved value — correct for consumers, wrong for configuration surfaces:
storing an override equal to the composition base leaves the resolved value
alone while changing what the document says (the field is now overridden, not
inherited) and moving every open editor's revision. `settings/document-updated
(ns, revision)` fires on any raw-section change, in-process or external, and
`host/settings-changed` now rides it.

That event also closes the stale model picker: editing a provider's `models`
changes no route, so `llm/adapters-updated` never fired and an open picker
kept serving the old catalog. A change to an exposed provider namespace now
emits `host/models-changed` too — that namespace holds the catalog.

Docs: both sides of the five touched README pairs, a type-equiv block for
`SettingsPathOp`, and an Agent Note recording what the plane exposes and who
may overwrite what. The deferred wire-redaction gaps (secrets behind
union/intersection/transform, `.default(...)` in the served envelope, schema
text in rejection messages, `new Function` rehydration, pi-ai's `headers`) are
recorded as TODO(settings-wire-redaction) and in Known Limitations rather than
half-fixed.

packages/client/schema-form/README.zh.md

@@ -18,5 +18,6 @@
 
 ## Known Limitations and Deferred Work
 
+- **重建 schema 会执行所收到的信封**——`rehydrateSchema` 会重建一个活的 schemastery 校验器，而 schemastery 通过 `new Function` 复活序列化过的 callback，因此 schema 信封是可执行内容，而非惰性数据。这只有在信封来自提供该页面的同一 host 时才可接受；面向浏览器的 schema 协议应当传递客户端无法执行的描述，此项与 settings seam 的[协议边界工作](../../settings/settings/README.md#known-limitations-and-deferred-work)一并暂缓。
 - **校验是草稿级的，而非逐字段**——`validateDraft` 报告 schemastery 的第一条失败消息（其中会点名 `$.path`）；逐字段的报错映射延后到出现需要它的消费方再做。
 - **没有通用渲染器**——一个 schema 驱动的表单组件曾被构建出来，随后被手写的 Models 编辑器取代（[Agent Note（agent 决策记录）](../../../.agents/notes/implemented/architecture/2026-07-30-web-config-plane.md)）；若未来有页面需要编辑任意分节，起点是这些辅助函数，而不是复活后的通用渲染器——除非该 note 的权衡发生变化。