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.

package.json

@@ -0,0 +1,17 @@
+{
+  "name": "peptide-e2e",
+  "version": "1.0.0",
+  "description": "Playwright smoke tests for peptiderepo.com (staging + production)",
+  "private": true,
+  "scripts": {
+    "test": "playwright test",
+    "test:staging": "BASE_URL=https://staging.peptiderepo.com playwright test",
+    "test:prod": "BASE_URL=https://peptiderepo.com playwright test",
+    "test:headed": "playwright test --headed",
+    "report": "playwright show-report"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.43.0",
+    "dotenv": "^16.4.5"
+  }
+}