refactor(client): replace the per-field settings preference controller with a namespace settings scope

bindSettingsScope mirrors the Host-side settings owner seam in the browser:
one scope per namespace publishes a snapshot store (status, section value,
revision, writability, host/memory mode), validates sections against the
namespace's serialized wire schema via dsh-client-schema-form, and keeps the
controller's listener-before-read, revisioned serialized writes, latest-wins
publication, conflict recovery, and disposal quiescence. Theme, locale, and
busy-Enter services now take the scope as a constructor collaborator, which
removes the bindPersistence/syncPreference two-phase callback pair and the
defaulted no-op persist writers; hand-written wire guards fall away in favor
of the registered schema. test-runtime gains a stubSettingsScope double.

packages/client/locale/tests/apply.spec.ts

@@ -9,6 +9,7 @@ import {
 } from '@deepseek-ai/dsh-client-locale/client'
 import type { LanguageRowInjected, LocaleService } from '@deepseek-ai/dsh-client-locale/client'
 import { LOCALE_SETTINGS_NAMESPACE } from '../src/locale-settings.ts'
+import { LocaleSettingsSchema } from '../src/index.ts'
 import { LanguageRow } from '../src/client/LanguageRow.tsx'
 import type { createLanguageRowStore } from '../src/client/settings-store.ts'
 
@@ -21,7 +22,7 @@ async function bench() {
   let revision = 0
   const namespace = () => ({
     ns: LOCALE_SETTINGS_NAMESPACE,
-    schema: {},
+    schema: LocaleSettingsSchema.toJSON(),
     value: preference === undefined ? {} : { preference },
     applies: 'live' as const,
     secrets: [],