test: authenticated admin E2E suite + accessibility + visual regression baselines

- Global setup: authenticates as admin, saves storageState for reuse
- playwright.config.ts: 3 projects (setup, authenticated, unauthenticated)
- authenticated-admin.spec.ts: 16 admin pages tested with real auth session
- accessibility.spec.ts: axe-core scans on all admin, public, and portal pages
- visual-regression.spec.ts: dark mode baselines for key pages (toHaveScreenshot)
- @axe-core/playwright added as devDependency
- .gitignore updated: excludes .auth/ and test-results/

Full suite: 262 tests passing (setup:1, authenticated:52, unauthenticated:209)

cannamanage-frontend/.gitignore

@@ -8,6 +8,10 @@
 
 # testing
 /coverage
+/e2e/.auth/
+/e2e/test-results/
+/e2e/**/*.png
+!/e2e/screenshots/
 
 # next.js
 /.next/