chore(agents): Add `dotagents`

[github-actions]

Note

The pull request "chore(agents): Add dotagents" was created by @chargome but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

• adds agents.toml for managing repo skills using https://github.com/getsentry/dotagents
• restructures existing skills to .agents folder

[linear]

JS-1810