Refactor workflow service boundaries

[YunaBraska]

Summary

• flatten workflow internals into clearer service/model boundaries
• remove dead helper/download/listener wrappers and tiny pass-through context classes
• keep workflow completion, validation, references, run UI, and cache behavior covered by the merged public-entrypoint tests

Why

The plugin had accumulated helper, logic, and service drawers for the same workflow flows. This PR keeps the behavior but trims the map so future changes have fewer places to hide.

Checks

• ./gradlew --no-daemon test --warning-mode all
• ./gradlew --no-daemon buildPlugin --warning-mode all
• ./gradlew --no-daemon compileJava compileTestJava --warning-mode all