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-conversation/src/index.ts

@@ -5,19 +5,16 @@ import z from 'schemastery'
 import { settingsNamespace } from '@deepseek-ai/dsh-settings'
 import {
   BUSY_ENTER_BEHAVIORS, BUSY_ENTER_FIELD, CONVERSATION_SETTINGS_NAMESPACE,
-  DEFAULT_BUSY_ENTER_BEHAVIOR, type BusyEnterBehavior,
+  DEFAULT_BUSY_ENTER_BEHAVIOR, type ConversationSettings,
 } from './submission-settings.ts'
 
 export {
   BUSY_ENTER_BEHAVIORS, BUSY_ENTER_FIELD, CONVERSATION_SETTINGS_NAMESPACE,
-  DEFAULT_BUSY_ENTER_BEHAVIOR, type BusyEnterBehavior,
+  DEFAULT_BUSY_ENTER_BEHAVIOR, type BusyEnterBehavior, type ConversationSettings,
 } from './submission-settings.ts'
 
-interface ConversationSettings {
-  busyEnter: BusyEnterBehavior
-}
-
-const ConversationSettingsSchema: z<ConversationSettings> = z.object({
+/** Durable conversation schema; also the wire envelope the browser scope validates against. */
+export const ConversationSettingsSchema: z<ConversationSettings> = z.object({
   [BUSY_ENTER_FIELD]: z.union([...BUSY_ENTER_BEHAVIORS]).default(DEFAULT_BUSY_ENTER_BEHAVIOR),
 })