feat: normalize commit message subjects

[marcus]

Summary

• add a commit-msg hook that normalizes type[(scope)]: summary (td-<id>) subjects
• preserve the final trailing task token when summaries mention other td-... ids
• document the canonical format and keep td: bump to vX.Y.Z as the explicit automated release exception

Verification

• bash ./scripts/test_commit-msg.sh
• make test-hooks
• go build -o td .
• env -u TD_FEATURE_SYNC_AUTOSYNC -u TD_FEATURE_SYNC_CLI go test ./...
• make install-hooks
• manual hook checks for scoped subjects and multi-token summaries