Simplify PRman for open-source contributors

[primorLee]

Summary

• focus PRman on ordinary developers contributing to well-known open-source projects
• replace technical packet output with a simple contribution preview
• shorten confirmation to CREATE DRAFT PR owner/repo while retaining internal scope binding
• update the Plugin and package to 0.5.0
• include the controlled confirmation-path validation from PR Validate denied and stale PR confirmations #1

Validation

• Python 3.11: 74 tests passed
• Python 3.12: 74 tests passed
• Skill validation passed
• Plugin validation passed
• wheel and sdist build passed