test(18): scope timezone e2e to desktop profile (fix harness cross-profile leak)

The timezone spec mutates the single household_timezone row, but e2e global-setup
resets it only once per run. Running on all three device profiles (iphone/pixel/
desktop) let one profile's "Save persists" write leak into another profile's
first-run assertions, failing the harness job in CI (workers=1, serial). The admin
timezone UI is desktop-focused, so skip the spec on non-desktop profiles — matching
the layout.spec.ts desktop-only pattern. Full harness: 107 passed, 19 skipped.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/pwa/e2e/timezone-verify.spec.ts

@@ -12,7 +12,12 @@
 import { test, expect } from '@playwright/test';
 
 test.describe('Admin Timezone section — 18-04 round-trip', () => {
-  test.beforeEach(async ({ page }) => {
+  test.beforeEach(async ({ page }, testInfo) => {
+    // Desktop-only: the admin timezone UI is desktop-focused, and these tests mutate
+    // the single household_timezone row. global-setup resets that row once per run, so
+    // running on multiple profiles lets one project's save leak into another project's
+    // first-run assertions. Restricting to one project keeps the shared state coherent.
+    test.skip(testInfo.project.name !== 'desktop', 'Admin timezone UI is desktop-only');
     await page.goto('/admin');
     await expect(page.getByRole('heading', { name: 'Admin Settings' })).toBeVisible();
     // Wait for the Timezone section to load (requires the 18-02 GET endpoint)