fix: handle empty staged files in pre-commit hook

[jmcte]

Summary

• Make the generated pre-commit hook safe when its staged-file list is empty under Bash set -u.
• Add a smoke test that invokes the generated hook from a clean feature branch.

Governing Issue

No governing issue is linked: this is a narrow hook reliability fix requested directly by Pheidon.

Validation

• npm test -- --run tests/smoke.test.ts tests/render.test.ts (30 tests passed)
• npm run typecheck
• git diff --check
• Agent-authored changes passed autoreview with no accepted or actionable findings.
• Required PR checks are expected to satisfy CI Gate.

Bootstrap Governance

• Changes are scoped to Bootstrap's generated hook and its regression coverage.
• Contributor guidance and managed-repository policy are not changed.
• No secrets, credentials, or machine-local state are introduced.

Material change: no

Merge Automation

• Auto-merge is not safe to arm before the required independent review is available.

Notes

The current hook dereferences an empty Bash array with set -u, which blocks a metadata-only amend such as adding a DCO trailer. The generated hook now expands the array zero-safely and skips the fallback empty entry.

[athena-omt]

Reviewed current head 0addaae locally. The empty-array guard correctly preserves hook behavior, and the new clean-feature-branch regression covers the failure path. Targeted smoke test and typecheck passed. Branch is current with main and mergeable, but Claude and Cloudflare check suites remain queued; deferring approval until CI settles.