feat: initial Playwright smoke suite

20 tests across 5 files covering all plugin surfaces on staging:
- Homepage load and PHP fatal detection
- Reconstitution Calculator shortcode + math
- Peptide Search AI widget + AJAX response
- Admin: all plugins active, PSA + PRAutoBlogger settings pages
- REST API: prc/v1/presets, peptides/v1/search, compounds, CPT types

Staging shortcode pages:
  /reconstitution-calculator/ - [prc_calculator]
  /search-peptides/           - [peptide_search]
  /peptide-directory/         - [peptide_directory]

GHA workflow: smoke.yml supports manual dispatch + workflow_call
for use as a deploy gate from plugin repos.

tests/00-homepage.spec.ts

@@ -0,0 +1,40 @@
+/**
+ * 00-homepage.spec.ts
+ *
+ * What: Verifies the site root loads with no fatal PHP errors and basic
+ *       theme elements are present. Catches theme activation failures,
+ *       white screens, and missing plugin-provided content.
+ * Who triggers it: Playwright chromium project (post-auth setup).
+ * Dependencies: peptide-starter-theme, PR Core active.
+ */
+
+import { test, expect } from '@playwright/test';
+
+test.describe('Homepage', () => {
+  test('loads with HTTP 200 and no fatal error', async ({ page }) => {
+    const response = await page.goto('/');
+    expect(response?.status()).toBe(200);
+  });
+
+  test('has no PHP fatal error or white screen', async ({ page }) => {
+    await page.goto('/');
+    const body = await page.textContent('body');
+    // PHP fatals produce these strings in non-production WP configs
+    expect(body).not.toContain('Fatal error');
+    expect(body).not.toContain('Parse error');
+    expect(body).not.toContain('Warning: ');
+    // White-screen: body is empty or nearly empty
+    expect((body ?? '').trim().length).toBeGreaterThan(200);
+  });
+
+  test('renders site name in page title', async ({ page }) => {
+    await page.goto('/');
+    await expect(page).toHaveTitle(/peptiderepo/i);
+  });
+
+  test('wp-admin bar present (logged-in session)', async ({ page }) => {
+    await page.goto('/');
+    // The auth state from global.setup means we should see the admin bar
+    await expect(page.locator('#wpadminbar')).toBeVisible();
+  });
+});