chore: Improve auto-response bot and fix GitHub Action warnings

[F16shen]

Summary

• refactor the GitHub auto-response workflow into a dedicated script and config file
• add first-time contributor welcomes, template compliance checks, and issue auto-classification
• align issue auto-classification labels with the existing labeler taxonomy and add prioritization/exclusivity rules
• fix GitHub Actions Node.js warning related workflow metadata updates

Testing

• validated the edited files with editor diagnostics
• did not run GitHub Actions locally