PR review: Analyze diffs and post review comments

[nev-offload]

Problem

When triggered by PR events, the agent should review the PR diff and post meaningful review comments.

Expected behavior

• On pull_request.opened or pull_request.synchronize, fetch the PR diff
• Pass the diff to the agent as context along with the repo's conventions
• Agent posts a PR review (not just a comment) with inline comments on specific lines
• Support approve/request-changes/comment review types

Implementation notes

• Use octokit.pulls.get() with mediaType: { format: "diff" } to get the diff
• Use octokit.pulls.createReview() to post structured reviews with line comments
• Include file context (not just the diff hunks) for better review quality
• Consider a .openclaw.yml config for review preferences (style, strictness, focus areas)
• Rate limit: don't review every push, maybe only on request or first push

Priority

P1 — Key feature for the GitHub App use case, but depends on #1 (response posting) being done first.

[nev-offload]

✅ Implemented in commit 99f7329

PR Review Features:

• Full diff analysis (fetches actual code changes, not just file list)
• Structured review output with VERDICT support
• Inline comments on specific lines via GitHub's native review system
• Position mapping (converts line numbers to diff positions)
• Graceful fallback to regular comments if review posting fails

How it works:

1. On PR open/update, fetches full diff via GitHub API
2. Sends diff + review instructions to agent
3. Parses agent response for structured format:

   VERDICT: approve | request_changes | comment
   
   ## Summary
   Overall review...
   
   ## Comments
   ### FILE: path/to/file.ts LINE: 42
   Specific feedback...
   

4. Posts as GitHub PR review with inline comments

Next up: #6 (Security review) → #8 (Marketplace publishing)