feat(hooks): normalize commit subjects

[marcus]

Summary

• add a local commit-msg hook that normalizes conventional commit subjects while preserving bodies and trailers
• install the new hook through make install-hooks and align repo-authored commit message sources with the same format
• document the normalized subject contract and verify it in a temporary git repo plus normal Go quality checks

Verification

• bash -n scripts/commit-msg.sh
• temporary git repo hook checks for valid, normalized, malformed, body/trailer, and release subjects
• go build ./...
• go vet ./...
• go test ./...