remove: broken Playwright E2E testing infrastructure

- Remove playwright.config.ts (references non-existent docker/docker-compose.yaml)
- Remove tests/e2e/ directory with broken test files
- Remove @playwright/test dependency from package.json
- Update documentation to remove E2E test references:
  - docs/architecture/PROJECT_STRUCTURE.md
  - docs/implementation/IMPLEMENTATION_SUMMARY.md
  - README.md
  - CONTRIBUTING.md
- E2E tests were non-functional due to missing Docker setup
- Focus on working unit and integration tests instead

package.json

@@ -40,7 +40,6 @@
     "@babel/core": "^7.28.4",
     "@babel/preset-env": "^7.28.3",
     "@babel/preset-typescript": "^7.27.1",
-    "@playwright/test": "^1.55.0",
     "@secretlint/node": "^11.2.3",
     "@secretlint/secretlint-rule-preset-recommend": "^11.2.3",
     "@testing-library/jest-dom": "^6.8.0",