test(18-04): playwright-cli timezone round-trip e2e spec

- 6 desktop tests covering the full 18-04 acceptance criteria:
  timezone section visible, combobox pre-filled, save disabled when
  unchanged, save enables on change, persists across reload, use-detected
  affordance sets browser zone
- All 6 pass against the real 18-02 API endpoints

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

@@ -0,0 +1,92 @@
+/**
+ * timezone-verify.spec.ts — 18-04 round-trip verification
+ *
+ * Verifies the admin Timezone section with the real 18-02 API endpoints.
+ * Runs on desktop profile only (admin UI is desktop-focused).
+ *
+ * NOTE: the IANA picker input is type="text" with list="iana-zones" which gives
+ * it the ARIA combobox role (not textbox) in Chromium.
+ */
+import { test, expect } from '@playwright/test';
+
+test.describe('Admin Timezone section — 18-04 round-trip', () => {
+  test.beforeEach(async ({ page }) => {
+    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)
+    const tzSection = page.getByRole('region', { name: 'Timezone' });
+    await expect(tzSection).toBeVisible({ timeout: 15_000 });
+  });
+
+  test('Timezone section is visible on /admin', async ({ page }) => {
+    await expect(page.getByRole('region', { name: 'Timezone' })).toBeVisible();
+  });
+
+  test('Timezone input (combobox) is visible and pre-filled', async ({ page }) => {
+    // ARIA role for <input type="text" list="iana-zones"> is combobox
+    const input = page.getByRole('combobox', { name: 'Household timezone' });
+    await expect(input).toBeVisible();
+    const val = await input.inputValue();
+    expect(val.length, 'Input should have a non-empty timezone').toBeGreaterThan(0);
+  });
+
+  test('Save button is disabled when timezone is unchanged', async ({ page }) => {
+    const tzSection = page.getByRole('region', { name: 'Timezone' });
+    const saveBtn = tzSection.getByRole('button', { name: /Save|Saving/ });
+    await expect(saveBtn).toBeVisible();
+    await expect(saveBtn).toBeDisabled();
+  });
+
+  test('Changing the input enables Save', async ({ page }) => {
+    const tzSection = page.getByRole('region', { name: 'Timezone' });
+    const input = page.getByRole('combobox', { name: 'Household timezone' });
+    await input.fill('America/Chicago');
+    const saveBtn = tzSection.getByRole('button', { name: /Save/ });
+    await expect(saveBtn).toBeEnabled();
+  });
+
+  test('Save persists timezone across reload', async ({ page }) => {
+    const input = page.getByRole('combobox', { name: 'Household timezone' });
+    const tzSection = page.getByRole('region', { name: 'Timezone' });
+
+    // Set to a known value
+    await input.fill('America/Chicago');
+    const saveBtn = tzSection.getByRole('button', { name: /^Save$/ });
+    await expect(saveBtn).toBeEnabled();
+    await saveBtn.click();
+    // Wait for save to complete (button re-disables when stored === input)
+    await expect(saveBtn).toBeDisabled({ timeout: 15_000 });
+
+    // Reload and verify persistence
+    await page.reload();
+    await expect(page.getByRole('heading', { name: 'Admin Settings' })).toBeVisible();
+    await expect(tzSection).toBeVisible({ timeout: 15_000 });
+    const inputAfterReload = page.getByRole('combobox', { name: 'Household timezone' });
+    await expect(inputAfterReload).toHaveValue('America/Chicago');
+
+    // system-default note should be gone after explicit set
+    await expect(tzSection.getByText('Using system default')).toHaveCount(0);
+  });
+
+  test('"Use detected" affordance sets input to browser zone', async ({ page }) => {
+    const tzSection = page.getByRole('region', { name: 'Timezone' });
+    const detectedBtn = tzSection.getByRole('button', { name: /Use detected:/ });
+
+    // The button is only visible when detected TZ != stored TZ
+    const count = await detectedBtn.count();
+    if (count === 0) {
+      test.skip();
+      return;
+    }
+
+    // Get the detected zone from the button label
+    const btnText = await detectedBtn.textContent();
+    const match = btnText?.match(/Use detected:\s*(.+)/);
+    const detectedZone = match?.[1]?.trim();
+    expect(detectedZone, 'Detected zone should be non-empty').toBeTruthy();
+
+    await detectedBtn.click();
+    const input = page.getByRole('combobox', { name: 'Household timezone' });
+    await expect(input).toHaveValue(detectedZone!);
+  });
+});