chore: add commit message normalizer

[marcus]

Summary

• Add a commit-msg hook that normalizes regular Conventional Commit subjects while preserving bodies and trailers.
• Add focused shell tests for normalization, passthrough subjects, trailer preservation, and invalid-subject rejection.
• Install both pre-commit and commit-msg hooks via git common-dir absolute symlinks, and align release docs/automation examples with the accepted format.

Validation

• bash scripts/test-commit-msg-hook.sh
• make install-hooks, then inspected /Users/marcus/code/td/.git/hooks/pre-commit and /Users/marcus/code/td/.git/hooks/commit-msg
• go test ./...
• git diff --check
• git diff --cached --check

Assumption

This standardizes future developer-local and automation commit subjects with a commit-msg hook rather than rewriting existing history.

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Automated by nightshift