Add OpenResty OPM ecosystem support

[AgentGoose32]

Summary

• add an OpenResty OPM ecosystem adapter using opm.openresty.org package pages
• support registry/documentation/download URLs, opm get install command, package lists, recently updated packages, package metadata, version metadata, and dependency metadata
• seed opm.openresty.org as the default OPM registry
• add model coverage for URLs, purl, package lists, metadata, versions, and dependencies

Refs #1227

Validation

• ruby -c app/models/ecosystem/opm.rb
• ruby -c test/models/ecosystem/opm_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.