fix(client): lint conformance for the preference services

Replace optional chains on always-present globals with the repo's
typeof guards (store.ts precedent), drop the non-null assertion by
failing loud on an impossible registry miss, and fix two arrow-parens
slips; cover the no-localStorage boot path in both service suites.

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

@@ -1,5 +1,5 @@
 // @vitest-environment jsdom
-import { beforeEach, describe, expect, it } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { Context } from 'cordis'
 import type { LocaleSnapshot } from '@deepseek-ai/dsh-client-locale/client'
 import { LocaleService, STORAGE_KEY } from '@deepseek-ai/dsh-client-locale/client'
@@ -80,6 +80,18 @@ describe('LocaleService', () => {
     expect(make().svc.getLocale().active).toBe('zh')
   })
 
+  it('runs without localStorage (node boots): defaults on read, no-op on write', () => {
+    vi.stubGlobal('localStorage', undefined)
+    try {
+      const { svc } = make()
+      expect(svc.getLocale().active).toBe('zh')
+      svc.setLocale('en')
+      expect(svc.getLocale().active).toBe('en')
+    } finally {
+      vi.unstubAllGlobals()
+    }
+  })
+
   it('exposes the two shipped locales with self-described labels', () => {
     const { svc } = make()
     expect(svc.getLocale().locales).toEqual([