* chore(contrib): add commit-msg hook, CODEOWNERS, team workflow docs
- Extend install-hooks.sh with commit-msg hook that enforces
Conventional Commits format on every commit
- Add .github/CODEOWNERS mapping packages, CI, scripts, and
security-sensitive files to @gsd-build/maintainers
- CONTRIBUTING.md: add Branching and commits section with naming
convention, commit format, and rebase guidance
- CONTRIBUTING.md: add Working with GSD section covering mode: team,
unique milestone IDs, and worktree isolation for multi-dev workflows
- CONTRIBUTING.md: surface npm run secret-scan:install-hook in Local
development with explanation of both hooks it installs
- CONTRIBUTING.md: align AI disclosure section — no AI tool authorship
in commits, Draft PR requirement for multi-phase agent work
* chore: remove install-hooks.sh — local git hook installation is too intrusive for a contributor PR
