Fix PR review agent to post inline comments and only review changed code

[derekmisler]

Fix PR review agent to (1) only comment on changed code and (2) post inline comments at the correct line numbers.

Problems

1. Reviewing existing code

The agent was finding bugs in existing code near the PR changes and reporting them. Example from PR #1391: flagged issues in Rerank() with note "existing code, not changed by this PR".

2. No inline comments

The agent used to post inline comments at specific lines but stopped doing so. All issues were dumped into the review body instead of being attached to the relevant lines.

Solution

Only review changed code

• Added "CRITICAL RULE" sections to root, drafter, and verifier agents
• Drafter explicitly told what NOT to report (existing code, nearby code, pre-existing issues)
• Verifier checks if code is actually changed before confirming
• Orchestrator only allows REQUEST_CHANGES for bugs in changed code

Restore inline comments

The old config had a single agent that directly posted. The multi-agent refactor broke the data flow.

Fixed by adding structured output format:

FILE: path/to/file.go
LINE: 123
SEVERITY: high
ISSUE: Brief description
DETAILS: Full explanation

• Drafter outputs this exact format with exact line numbers (not "around line X")
• Verifier preserves format, adds VERDICT field
• Orchestrator has clear instructions for converting to gh api JSON