Fix text clarity in lint-actions help and quick-setup dry-run output

[github-actions]

Summary

This PR implements 2 concrete text fixes from #2210:

1. Makefile wording accuracy
   • lint-actions help text now says Validate Claude workflow composite action files.
   • lint-actions runtime message now says Validating Claude workflow composite action files....
2. quick-setup dry-run accuracy
   • Updated dry-run checkout message to reflect actual conditional behavior (checkout existing branch or create from origin/$default_branch).

Validation

bash -n scripts/quick-setup.sh
make help | grep -E "lint-actions|Validate Claude workflow composite action files"
make compile && make lint

Notes

The remaining typo in .github/workflows/gh-aw-mention-in-issue.md (instructred → instructed) was not included because workflow-file pushes are restricted in this execution context. I posted the exact maintainer follow-up step on #2210.

Refs #2210

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What is this? | From workflow: Trigger Text Auditor

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