chore: migrate open PRs to new label taxonomy

[andreahlert]

Part of #690

Go through all open PRs and apply the new label taxonomy.

For each PR

1. Add kind/* and area/*
2. Add pr/stale to PRs with no activity for 14+ days after review
3. Add pr/do-not-merge to PRs that need significant rework
4. Convert truly inactive PRs (6+ months) to draft with a comment
5. Remove old labels

Current PR backlog

• 15 dependabot security bumps untouched for months
• 11 draft PRs from elijahbenizzy dating back to 2024
• Contributor PRs from 2024 with no review (Added Favicon #401, Update Instructor + Gemini example #267, WIP for tools #143)