Add Amazon ECR Public package support

[AgentGoose32]

Summary

• add Amazon ECR Public support to the Docker ecosystem integration
• seed gallery.ecr.aws as a non-default Docker registry
• map ECR Public package metadata, package names, install commands, registry URLs, and image tags via the public Gallery APIs
• add model coverage for the new ECR Public path

Refs #336

Validation

• ruby -c app/models/ecosystem/docker.rb
• ruby -c db/seeds.rb
• ruby -c test/models/ecosystem/docker_test.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.