chore: add Playwright E2E coverage with Codecov integration

Integrate @bgotink/playwright-coverage for E2E test coverage tracking:

Install @bgotink/playwright-coverage package
Update playwright.config.js with coverage reporter
Update test file imports to use coverage-enabled test function
Add e2e-tests.yml coverage artifact upload and merge job
Create codecov.yml with e2e flag configuration
Add E2E coverage skill and VS Code task
Coverage outputs: HTML, LCOV, JSON to coverage/e2e/
CI uploads merged coverage to Codecov with 'e2e' flag

Enables unified coverage view across unit and E2E tests

frontend/e2e/tests/security-mobile.spec.ts

@@ -5,7 +5,7 @@
  * Tests mobile viewport (375x667), tablet viewport (768x1024),
  * touch targets, scrolling, and layout responsiveness.
  */
-import { test, expect } from '@playwright/test'
+import { test, expect } from '@bgotink/playwright-coverage'
 
 const base = process.env.CHARON_BASE_URL || 'http://localhost:8080'
 

frontend/e2e/tests/waf.spec.ts

@@ -1,4 +1,4 @@
-import { test, expect } from '@playwright/test'
+import { test, expect } from '@bgotink/playwright-coverage'
 
 const base = process.env.CHARON_BASE_URL || 'http://localhost:8080'