fix(locale): gate browser detection on window and tolerate a missing languages list

Node >= 21 exposes a global `navigator` reporting the machine's own language,
so gating detection on `navigator` let a non-browser boot of the client tree
resolve to `en` instead of the documented fallback; `window` is the browser
test. `navigator.languages` is spec-required but absent on some embedders and
older WebViews, where spreading it would throw at boot, so the walk tolerates
its absence and `navigator.language` covers that host.

The per-spec pin boilerplate collapses into one suite-level
`usePinnedBrowserLanguages('zh-CN')`, which owns the rationale in
dsh-client-test-runtime, and the English-browser e2e scenario now clears the
console warnings channel too — its page has no closing inventory spec.

apps/web/tests/settings-chrome.e2e.ts

@@ -232,7 +232,10 @@ describe('web e2e: settings modal and General preferences', () => {
       const dialog = enPage.getByRole('dialog', { name: 'Settings' })
       await dialog.waitFor({ timeout: 10_000 })
       await dialog.getByRole('button', { name: 'English' }).waitFor({ timeout: 10_000 })
+      // This page has no closing inventory spec to sweep its console, so the
+      // scenario clears both tripwire channels itself.
       expect(enTripwire.pageErrors).toEqual([])
+      expect(enTripwire.warnings).toEqual([])
     } finally {
       await enPage.close()
     }