Add tested user documentation site and GitHub Pages deployment

[vitormattos]

Summary

This PR now follows the minimal maintenance approach:

• keep onboarding/documentation in README.md
• keep runnable examples under examples/
• keep automated example validation via PHPUnit (tests/Documentation/ExamplesTest.php)
• remove MkDocs/GitHub Pages/Python documentation stack

What changed (minimal mode)

Kept

• README.md as the primary user entry point
• examples/* and examples/assets/*
• tests/Documentation/ExamplesTest.php
• PHPUnit documentation testsuite (for example checks)

Removed

• MkDocs configuration and dependencies:
  • mkdocs.yml
  • requirements-docs.txt
• docs site source tree:
  • docs/
• docs drift script:
  • scripts/check-docs-drift.php
• docs deployment workflow:
  • .github/workflows/docs.yml

Composer scripts

Removed docs-stack scripts and kept example-test script:

• removed: docs:check-drift, docs:build, docs:serve, docs:test
• kept equivalent validation intent through: examples:test

Validation executed

• docker compose run --rm php bash -lc "composer run examples:test"
• docker compose run --rm php bash -lc "composer validate --strict"

Notes

This update is intentionally pragmatic to reduce long-term maintenance overhead while preserving executable, tested usage examples.