docs: document Git hook env sanitization

[BenSheridanEdwards]

What changed

• Documents the Git hook environment hazard for tests that create or inspect other Git repositories.
• Adds the unset $(git rev-parse --local-env-vars) pattern to the quality-gates skill and installer skill.
• Keeps the template hook unchanged; this is a conditional pattern for target repos that need it.

Proof

pnpm verify
Checked 28 files in 191ms. No fixes applied.
✓ No issues in 4 changed files (0.64s)
Test Suites: 3 passed, 3 total
Tests:       11 passed, 11 total
✓ built in 760ms
app bundle (JS, brotli): 52.83 kB / 80 kB
app styles (CSS, brotli): 697 B / 5 kB

pnpm e2e
2 passed (5.5s)

git commit -m "docs: document Git hook env sanitization"
› typecheck
› biome (lint + format + imports, staged only)
› fallow (code intelligence: dead code, cycles, complexity)
✓ No issues in 4 changed files (0.18s)
› secret scan (gitleaks, staged content)
INF no leaks found

git push -u origin codex/chore/git-hook-env-quality-gates
Test Suites: 3 passed, 3 total
Tests:       11 passed, 11 total
✓ built in 433ms
2 passed (4.3s)

Screenshots / visual proof: N/A, documentation and skill guidance only.

Checklist

• Local proof is included above.
• GitHub Actions will be checked on this PR before merge.
• Screenshots or StyleProof evidence are included, or marked N/A with a reason.
• No private project facts, secrets, or local paths are included.

[github-actions]

Fallow audit report

Found 1 finding.

Details

Severity	Rule	Location	Description
minor	fallow/unused-dev-dependency	package.json:44	Package '@lhci/cli' is in devDependencies but never imported

Generated by fallow.

[github-actions]

Fallow audit report

0 inline findings selected for GitHub review.

[github-actions]

🗺️ StyleProof report

✓ No visual changes detected.