fix(web): persist theme preference in settings

packages/client/ui-theme/src/index.ts

@@ -1,4 +1,35 @@
-/** Host loader entry for the browser implementation exported from `./client`. */
+/** Host registration for the browser theme preference. */
 
-/** Host plugin body — no host-side behavior for the theme plugin. */
-export function apply(): void {}
+import type { Context } from 'cordis'
+import z from 'schemastery'
+import { settingsNamespace } from '@deepseek-ai/dsh-settings'
+import {
+  DEFAULT_PREFERENCE, THEME_PREFERENCE_FIELD, THEME_SETTINGS_NAMESPACE,
+  type ThemePreference,
+} from './theme-settings.ts'
+
+export {
+  DEFAULT_PREFERENCE, THEME_PREFERENCE_FIELD, THEME_SETTINGS_NAMESPACE,
+  type ThemePreference,
+} from './theme-settings.ts'
+
+interface ThemeSettings {
+  preference: ThemePreference
+}
+
+const ThemeSettingsSchema: z<ThemeSettings> = z.object({
+  [THEME_PREFERENCE_FIELD]: z.union(['light', 'dark', 'system']).default(DEFAULT_PREFERENCE),
+})
+
+/**
+ * Register the durable theme section when a settings provider exists.
+ * @param ctx - Host context whose optional settings service owns the section.
+ */
+export function apply(ctx: Context): void {
+  ctx.inject(['settings'], (settingsCtx) => {
+    settingsCtx.settings.register(
+      settingsNamespace(THEME_SETTINGS_NAMESPACE),
+      ThemeSettingsSchema,
+    )
+  })
+}