refactor(engine): maxBuffer and --dangerously-skip-permissions duplicated as inline literals across both CLI spawn sites (staging review — PR #2018)

[rapiercraft-forgedock]

Problem

maxBuffer: 50 * 1024 * 1024 and the "--dangerously-skip-permissions" flag are duplicated as inline literals in both runner.mjs runCliBackend and init-enrich-cli.mjs, rather than a shared named constant/helper.

Given SEC-1 and BUG-2 both concern that flag, centralising it would make the security posture reviewable in one place.

Source: PR #2018 (staging → main deploy review) — finding QA-3
Location: bin/init-enrich-cli.mjs:148
Confidence: POSSIBLE
Severity: LOW

Source Branch Context

Code branch: staging
Worktree base: origin/staging

When fixing: git worktree add ../fix-{slug} -b fix/{slug} origin/staging

Acceptance Criteria

• Finding validated: VALIDATED / FALSE_POSITIVE / INCONCLUSIVE
• If VALIDATED: fix implemented and tested on origin/staging
• Regression test added covering this path