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/ui-theme/src/index.ts

@@ -5,19 +5,16 @@ import z from 'schemastery'
 import { settingsNamespace } from '@deepseek-ai/dsh-settings'
 import {
   DEFAULT_PREFERENCE, THEME_PREFERENCE_FIELD, THEME_PREFERENCES, THEME_SETTINGS_NAMESPACE,
-  type ThemePreference,
+  type ThemeSettings,
 } from './theme-settings.ts'
 
 export {
   DEFAULT_PREFERENCE, THEME_PREFERENCE_FIELD, THEME_PREFERENCES, THEME_SETTINGS_NAMESPACE,
-  type ThemePreference,
+  type ThemePreference, type ThemeSettings,
 } from './theme-settings.ts'
 
-interface ThemeSettings {
-  preference: ThemePreference
-}
-
-const ThemeSettingsSchema: z<ThemeSettings> = z.object({
+/** Durable theme schema; also the wire envelope the browser scope validates against. */
+export const ThemeSettingsSchema: z<ThemeSettings> = z.object({
   [THEME_PREFERENCE_FIELD]: z.union([...THEME_PREFERENCES]).default(DEFAULT_PREFERENCE),
 })