Atlas is now a plain library plus a tiny web app with no framework:

- p3k\Atlas\App routes the seven endpoints, p3k\Atlas\View renders the
  plain PHP templates, p3k\Atlas\Response carries the result. Controllers
  are ported line for line from the Slim closures.
- p3k\geo\StaticMap\render() returns the image bytes and content type
  instead of sending headers and echoing, so other apps can embed it.
  generate() remains as a wrapper. The tile size constant is namespaced.
- Fix Airports::from_code() (the file handle was never kept) and the
  reference to a Geocoder class that never existed.
- composer: type library, PHP 8.1+, ext-gd required; lib/helpers.php is no
  longer autoloaded so nothing global leaks into consumers.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LeX8DR83QNwGUBJDAXj8fi

closes #2

geocoding and timezone works