- Add 'pypi' package type to config.py; simple/ paths are mutable by default
- Refactor content-type detection into _get_content_type() helper; add .whl
- Add _resolve_content() which rewrites files host URLs in simple index HTML
to go through the proxy (pypi_files_url / pypi_files_remote config keys),
and returns text/html content-type for simple index responses
- Add basic auth support for non-Docker remotes (username + password/token
in remote config); thread auth through _upstream_reachable and
check_upstream_changed so mutable TTL checks also authenticate
- Add 'pypi' remote (pypi.org simple index) and 'pypi-files' remote
(files.pythonhosted.org) to remotes.yaml; add 'pypi-gitea' example for
Gitea package registries where index and files share the same base URL
- Add unit tests: simple index URL rewriting, HTML content-type, .whl/.tar.gz
content-types, mutable index detection, and immutable pattern enforcement
unkinben