Add AGENTS.md

[alltheseas]

Summary

• Add AGENTS.md documenting expectations for automation agents contributing to Damus.

Checklist

• I have read (or I am familiar with) the Contribution Guidelines
• I have tested the changes in this PR
• I have opened or referred to an existing github issue related to this change.
• My PR is either small, or I have split it into smaller logical commits that are easier to review
• I have added the signoff line to all my commits. See Signing off your work
• I have added appropriate changelog entries for the changes in this PR. See Adding changelog entries
  • I do not need to add a changelog entry. Reason: Documentation-only addition for automation agents.
• I have added appropriate Closes: or Fixes: tags in the commit messages wherever applicable, or made sure those are not needed. See Submitting patches

Test report

Device: N/A – documentation-only change

iOS: N/A

Damus: dd3634b

Setup: Documentation content only

Steps: No runtime changes to exercise

Results:

• PASS
• Partial PASS
  • Details: N/A
• Not Run
  • Details: Documentation-only change; no tests required.

Other notes

• Ported upstream commit dd3634b as-is so the fork exposes agent guidance publicly.

[danieldaquino]

The document doesn't contain all info that an AI might need, but is a good start; we can continue to add more as we learn more about using AI agents around the codebase.

Added one inline comment to be addressed.

In terms of guidelines, can you please add the sign-off line to your commit?

Thank you!

[danieldaquino]

The link https://github.com/damus-io/damus/tree/master/nostrdbm is broken

Perhaps you meant this?

Suggested change

	Damus is an iOS client built around a local relay model ([damus-io/damus#3204](https://github.com/damus-io/damus/pull/3204)) to keep interactions snappy and resilient. The app operates on `nostrdb` ([source](https://github.com/damus-io/damus/tree/master/nostrdbm)), and agents working on Damus should maximize usage of `nostrdb` facilities whenever possible.
	Damus is an iOS client built around a local relay model ([damus-io/damus#3204](https://github.com/damus-io/damus/pull/3204)) to keep interactions snappy and resilient. The app operates on `nostrdb` ([source](https://github.com/damus-io/damus/tree/master/nostrdb)), and agents working on Damus should maximize usage of `nostrdb` facilities whenever possible.