docs(maintainers): add agent directives for types packages

[zimeg]

Summary

This PR adds AGENTS.md to the @slack/types package 🎁

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 667a944

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[zimeg]

📚 No changes were requested after an /init with this changeset and I'll merge this now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.41%. Comparing base (04064a9) to head (667a944).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2557   +/-   ##
=======================================
  Coverage   87.41%   87.41%           
=======================================
  Files          62       62           
  Lines       10251    10251           
  Branches      415      415           
=======================================
  Hits         8961     8961           
  Misses       1269     1269           
  Partials       21       21           

Flag	Coverage Δ
cli-hooks	87.41% <ø> (ø)
cli-test	87.41% <ø> (ø)
logger	87.41% <ø> (ø)
oauth	87.41% <ø> (ø)
socket-mode	87.41% <ø> (ø)
web-api	87.41% <ø> (ø)
webhook	87.41% <ø> (ø)

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