Add automated issue triage workflow

[binaricat]

Summary

• classify new issues into the five agreed outcomes
• implement and repeatedly review focused bugs and quick features
• defer uncertain or oversized work with a short reply
• continue questions and planning topics in Discussions
• send Slack progress notifications and isolate automatic branches from repository secrets

Setup still required

Before enabling the workflow, add OPENAI_API_KEY, TRIAGE_GITHUB_TOKEN, and SLACK_WEBHOOK_URL to the repository Actions secrets.

Validation

• full test suite
• lint
• production build
• 13 focused triage tests
• workflow validation
• repeated Codex review/fix cycles, ending with no findings