[gouyt13]

Summary

The CI routing update in #114 correctly selected every check on the PR, but selected them again on its merge push to main. The second run repeated C++ platform builds, sanitizers, and Python package builds even though the merge changed only routing files and Markdown.

This change keeps broad validation for routing PRs. On a tagged main version, a push containing only the routing files and Markdown selects Python quality, which runs the selector tests, without repeating platform builds. Mixed source changes and untagged versions retain full selection; the latter preserves the automatic release gate.

Verification

• 22 CI and release unit tests passed
• Ruff formatting and linting passed for .github/scripts
• ./scripts/check-python.sh passed using the project environment's Ruff
• Replayed the Run CI checks only for affected files #114 merge diff: selected checks changed from all groups to python_quality
• git diff --check passed