llm: add mz-dev, mz-test, mz-debug, mz-commit skills

[antiguru]

Add Claude Code skills for developing, testing, debugging, and committing in the Materialize repository.
Split into focused skills that trigger independently.

🤖 Generated with Claude Code

[github-actions]

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[djahandarie]

(This is nice for external contributors too! 😄 )

[mtabebe]

I am directionally aligned on this. I'll close my test skill PR.

Two minor comments.

[mtabebe]

🚢 LGTM

[antiguru]

Thanks for the reviews!

[def-]

If mzcompose keeps rebuilding even if a CI image is available, make sure the src/ directory is clean. Untracked files are also considered as part of the image tag.