feat: replace mkdocs with pdoc for API docs, add pytest-html-plus with BDD docstrings

[nullhack]

Summary

• Replace mkdocs/mkdocstrings with pdoc for API documentation
• Add pytest-html-plus for BDD-style HTML test reports
• Update conftest.py to extract and display Given/When/Then docstrings in HTML
• Add doc-publish task to push API docs to GitHub Pages

Changes

Documentation

• pyproject.toml: Replace pdoc dependencies, update doc-serve/doc-build/doc-publish tasks
• README.md: Update doc commands, change coverage path to docs/coverage

Testing

• Add tests/conftest.py with BDD docstring extraction and HTML regeneration
• Update pyproject.toml for pytest-html-plus with JSON report
• Add BDD docstring guidelines to TDD skill

Removed

• Delete docs/mkdocs.yaml and docs/docs/ (mkdocs config)
• Remove mkdocs dependencies from pyproject.toml

[nullhack]

PR Review

Verified the following changes work correctly:

Template Generation

• cookiecutter generates project successfully with all new files

Dependencies

• pdoc, pytest-html-plus, pytest-mock installed correctly

Tests

• task test passes with 10 tests, 100% coverage
• BDD docstrings display in HTML report (19 occurrences of 'Given:')
• Line breaks render correctly (<br> in HTML)

Documentation

• task doc-build generates docs/api/index.html with search
• task doc-serve serves pdoc locally
• README updated with new doc commands

Code Quality

• No linting issues

Recommendation: Merge and release.