docs: add datacommons-pr-review skill document and register it in AGENTS.md

[nick-nlb]

Overview

This PR adds in the datacommons-pr view skill and registers it with AGENTS.md

We will continue to update and fine-tune the skill as we use it.

Changes Made

• Adds in the PR review skill
• Registers it with agents.

Testing Done

This PR only updates documentation; no testing is required.

Risk & Rollback

This PR only updates documentation. There is no risk or required rollback scenario.

Follow-ups

Once this PR is merged into main, we will back-merge it into narratives-dev.

Checklist

• I have read AGENTS.md and followed CODING_GUIDELINES.md, plus
  FRONTEND.md for UI changes. [NOT APPLICABLE]
• I have run the app's lint, test, and build commands, as documented in
  that application's guide. [NOT APPLICABLE]
• I have commented my code, particularly in hard-to-understand areas. [NOT APPLICABLE]
• My changes generate no new warnings.

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Note: Only Maintainers can approve and merge PRs. Expected initial review
time: 3 business days.

[gemini-code-assist]

Code Review

This pull request introduces a new PR review workflow and verification checklist in .agent/skills/datacommons-pr-review/SKILL.md and registers it in the root AGENTS.md file. The review feedback suggests a minor formatting improvement to ensure consistent backtick usage for file references in the documentation.

[beets]

thanks for adding this! excited to see this unify our PR reviews