[zeroecco]

Summary

• Adds .githooks/commit-msg that rejects commits whose subject line does not match ZIR-NNN: <non-empty description> (Merge/Revert commits are exempt)
• Adds .githooks/prepare-commit-msg that auto-prepends ZIR-000: when the prefix is absent; skips merge, squash, and template commit sources so pre-populated messages are never garbled
• Adds scripts/setup-hooks.sh for one-command developer opt-in (git config core.hooksPath .githooks)
• Adds .github/workflows/commit-lint.yml that enforces the same pattern as the local hook on every PR — ^ZIR-[0-9]+: .+ — so CI catches any misses
• Adds CONTRIBUTING.md documenting the format and setup steps

Design decisions

• Single hook system only (.githooks/ + core.hooksPath). No duplicate hooks/ directory or second setup script.
• CI and local hook use identical regex so a commit cannot pass one and fail the other.
• prepare-commit-msg skips the template COMMIT_SOURCE to avoid prepending ZIR-000: onto a ZIR-XXX: template placeholder.
• No unused variables passed into awk.

Test plan

• Run bash scripts/setup-hooks.sh in a clone; verify git config core.hooksPath returns .githooks
• Attempt git commit -m "no prefix" — should be rejected by commit-msg hook
• Attempt git commit -m "ZIR-123: valid" — should succeed
• Attempt git commit -m "ZIR-123: " (empty description) — should be rejected
• Verify Merge branch foo is accepted
• Open a PR with a non-conforming commit and confirm the CI workflow fails

Nightshift-Task: commit-normalize
Nightshift-Ref: https://github.com/marcus/nightshift