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.

.env.example

@@ -0,0 +1,9 @@
+# Copy this to .env and fill in values — never commit .env to git
+BASE_URL=https://staging.peptiderepo.com
+WP_ADMIN_USER=peptiderepo
+WP_ADMIN_PASSWORD=your-staging-password-here
+
+# Page paths where shortcodes live (adjust to match actual WP page slugs)
+CALC_PAGE_PATH=/reconstitution-calculator/
+SEARCH_PAGE_PATH=/search-peptides/
+DIRECTORY_PAGE_PATH=/peptide-directory/