refactor: complete monorepo with extension in packages/

[recca0120]

Summary

• Extract PHPUnit domain layer into packages/phpunit/ workspace package
• Move VS Code extension into packages/extension/ workspace package
• Root package.json now serves only as workspace orchestrator
• Each package owns its own tsconfig.json, vitest.config.ts, and biome.json
• Remove unnecessary root configs (tsconfig.json, vitest.config.ts, biome.json, qodana.yaml, vsc-extension-quickstart.md)
• Update CI workflows (tests.yml, e2e.yml, publish.yml) for new paths
• Update .vscode/launch.json and tasks.json for new structure

Test plan

• pnpm install succeeds
• pnpm -r run typecheck passes for both packages
• pnpm -r run lint passes for both packages
• pnpm -r run test — phpunit (561 tests), extension (344 tests) all pass
• node packages/extension/esbuild.mjs builds successfully
• vsce package --no-dependencies produces valid VSIX
• CI workflows pass on GitHub Actions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.13%. Comparing base (d7c6158) to head (a4b16f1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #372      +/-   ##
==========================================
- Coverage   93.45%   91.13%   -2.32%     
==========================================
  Files          85       85              
  Lines        4184     4184              
  Branches      918      918              
==========================================
- Hits         3910     3813      -97     
- Misses        246      329      +83     
- Partials       28       42      +14     

Flag	Coverage Δ
unittests	91.13% <100.00%> (-2.32%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.