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.

global.setup.ts

@@ -0,0 +1,42 @@
+/**
+ * global.setup.ts
+ *
+ * What: Authenticates to WordPress admin once and persists the session to disk.
+ * Who triggers it: Playwright "setup" project, runs before all smoke tests.
+ * Dependencies: WP_ADMIN_USER and WP_ADMIN_PASSWORD env vars.
+ *
+ * The saved auth state (playwright/.auth/admin.json) is reused by the
+ * "chromium" project so individual tests don't each incur a login round-trip.
+ */
+
+import { test as setup, expect } from '@playwright/test';
+import * as path from 'path';
+import * as fs from 'fs';
+
+const AUTH_FILE = path.join(__dirname, 'playwright/.auth/admin.json');
+
+setup('authenticate as WP admin', async ({ page }) => {
+  const user = process.env.WP_ADMIN_USER;
+  const password = process.env.WP_ADMIN_PASSWORD;
+
+  if (!user || !password) {
+    throw new Error(
+      'WP_ADMIN_USER and WP_ADMIN_PASSWORD must be set in .env or CI secrets'
+    );
+  }
+
+  // Ensure directory exists
+  fs.mkdirSync(path.dirname(AUTH_FILE), { recursive: true });
+
+  await page.goto('/wp-login.php');
+  await page.fill('#user_login', user);
+  await page.fill('#user_pass', password);
+  await page.click('#wp-submit');
+
+  // Wait for successful redirect to wp-admin dashboard
+  await expect(page).toHaveURL(/wp-admin/, { timeout: 20_000 });
+  await expect(page.locator('#wpadminbar')).toBeVisible();
+
+  // Persist session cookies + localStorage to disk
+  await page.context().storageState({ path: AUTH_FILE });
+});