chore(hooks): normalize commit subjects

[marcus]

Summary

• add a repo-managed commit-msg validator for conventional-style commit subjects
• install pre-commit and commit-msg as wrapper hooks in Git's active hooks directory so core.hooksPath and linked worktrees stay safe
• document the commit format and hook behavior in the development README

Testing

• smoke-test valid and invalid commit subjects with scripts/commit-msg.sh
• smoke-test make install-hooks with default hooks, temporary core.hooksPath, and a linked worktree that is removed after installation
• go test ./...

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