Add Drupal module ecosystem support

[AgentGoose32]

Summary

• add a Drupal module ecosystem adapter backed by the drupal.org JSON API
• support registry/documentation/download URLs, Composer install command, module lookup, package lists, recently updated packages, and version metadata
• seed drupal.org as the default Drupal registry
• add model coverage for URLs, purl, module lists, metadata, downloads, and versions

Refs #980

Validation

• ruby -c app/models/ecosystem/drupal.rb
• ruby -c test/models/ecosystem/drupal_test.rb
• ruby -c db/seeds.rb
• git diff --check

Full Rails test execution is blocked locally because this repo lockfile requires Bundler 4.0.10 while the system Ruby/Bundler cannot satisfy it.