feat: replace Playwright E2E tests with Karma functional tests for CMCD v2

Replace the Playwright-based E2E test suite with Karma functional tests
that use XHR interceptors to validate CMCD v2 spec compliance. This
eliminates the @playwright/test dependency (~100MB) while maintaining
full test coverage across all three transmission modes (query, header,
event), key filtering, and version validation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: littlespex

package.json

@@ -38,8 +38,6 @@
     "prepare": "node githook.cjs",
     "start": "webpack serve --config build/webpack/modern/webpack.modern.dev.cjs",
     "test": "karma start test/unit/config/karma.unit.conf.cjs",
-    "test-e2e": "npx playwright test --config test/e2e/playwright.config.js",
-    "test-e2e:headed": "npx playwright test --config test/e2e/playwright.config.js --headed",
     "test-functional": "karma start test/functional/config/karma.functional.conf.cjs --configfile=local --streamsfile=smoke",
     "webpack-build-legacy": "webpack --config build/webpack/legacy/webpack.legacy.prod.cjs",
     "webpack-build-modern": "webpack --config build/webpack/modern/webpack.modern.prod.cjs"
@@ -53,7 +51,6 @@
     "@babel/runtime": "^7.28.4",
     "@chiragrupani/karma-chromium-edge-launcher": "^2.4.1",
     "@eslint/js": "^9.39.1",
-    "@playwright/test": "^1.58.2",
     "babel-loader": "^10.0.0",
     "babel-plugin-istanbul": "^7.0.1",
     "baseline-browser-mapping": "^2.10.0",