Add baseline cluster metrics to clustering summary table

[cmccomb]

Summary

• compute baseline cluster counts and noise totals during training
• display baseline metrics alongside homogeneity/completeness/v-measure in the clustering summary
• add regression tests to ensure baseline information appears without ground-truth labels

Testing

• cargo fmt
• cargo clippy --all-targets -- -D warnings -D clippy::pedantic
• cargo test

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Codex Task