Checkpoint Validation Improvements

2025-11-13: Fixed mkdocs strict mode validation

Enhanced checkpoint.sh to validate BOTH user and developer documentation builds: - User docs (mkdocs.yml) with --strict mode - Developer docs (mkdocs-dev.yml) with --strict mode

Both builds now check for warnings that cause GitHub deployment failures: - Unrecognized relative links - Missing anchors - Absolute links

This prevents commits with broken documentation links from reaching production.