P4: `/react-review` on diff + 1-hop neighbors

[tkowalczyk]

Parent PRD

#1

What to build

A new skill, /react-review, that scans only the changed files on the current branch versus a base branch (default main), expanded by 1-hop import neighbors — files that import or are imported by the changed files. Reuses Rule Card Library, Code Scanner, and Issue Manager unchanged. Adds a thin per-skill component (Diff Scanner) that computes the file set.

If a PR exists for the current branch, the skill records that context in the issue body. If no PR exists, the skill opens a standalone issue with the branch ref in the title.

All issue lifecycle behaviors from P3 apply: dedup by label, in-place body update, regression as a new issue with backlink.

See PRD #1 "Implementation Decisions" → "Scanning strategies" for the diff/1-hop scope rules.

Acceptance criteria

• skills/react-review/SKILL.md exists with manual-trigger metadata
• Skill correctly identifies changed files via git diff --name-only <base>...HEAD
• 1-hop import neighbors are added to the scan set via static import analysis (files importing or imported by changed files)
• Excluded directories (matching the smart-scan exclusion list from P2b) are never scanned
• On a branch with no open PR, a standalone issue is created with the branch ref in the title
• On a branch with an open PR, the issue body links to the PR
• All issue lifecycle behaviors from P3 work for /react-review issues
• Reuses Rule Card Library, Code Scanner, and Issue Manager from earlier phases without forking them

Blocked by

• Blocked by P3: Re-run lifecycle (full Issue Manager) #6

User stories addressed

• User story 3
• User story 4
• User story 25