## Summary
Add per-job `if:` gates so deployments that don't want — or can't run —
these jobs can switch them off via repository variables, without editing
workflows.
- `ENABLE_CLAUDE_CODE` gates the Claude jobs: interactive `@claude`, the
CLAUDE.md audit, and the REVIEW.md drift audit.
- `ENABLE_WORKFLOW_SECURITY_SCAN` gates the Zizmor job, which uploads
SARIF and so needs GitHub code scanning enabled.
Both default to **enabled**: a job runs unless its variable is
explicitly set to `'false'`, so behaviour is unchanged anywhere the
variables are unset. The sibling `actionlint` job and the report-only
Trivy scan are untouched.
## Test plan
- [x] `actionlint` clean on the four edited workflows
- [x] YAML parses for all four files
Daniel Sutton
f073d8708a