Update bounties page for agent-compatible tasks

[vinaykrsinghal-stage]

Summary

• Adds agent-compatible bounty guidance to the bounties mechanism page
• Calls out reviewable task types, eligibility/submission guardrails, and payout-claim clarity
• Adds the Gitcoin research article on AI agents and public goods as further reading

Closes #360

Validation

• Parsed src/content/mechanisms/bounties.md front matter with gray-matter
• Checked the new Gitcoin research link returns HTTP 200
• Ran git diff --check

Note: I did not run a full Next build because the full partial-clone checkout stalled while fetching the complete repository; this is a one-file Markdown content update.

[vercel]

@vinaykrsinghal-stage is attempting to deploy a commit to the Allo Capital Team on Vercel.

A member of the Team first needs to authorize it.