feat(validation): archive key result assets

Keep key validation outputs and analysis tables tracked directly,
package analysis plot PNGs into a small tar.gz backup, and add
analysis scripts plus tests so the stored results remain
reproducible without flooding git with large image trees.

tests/validation/test_fragment_library_analysis.py

@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+import pandas as pd
+import pytest
+
+from macro_lactone_toolkit.validation.fragment_library_analysis import (
+    build_position_diversity_table,
+    count_non_dummy_atoms,
+)
+
+
+def test_count_non_dummy_atoms_excludes_dummy_atoms() -> None:
+    assert count_non_dummy_atoms("*O") == 1
+    assert count_non_dummy_atoms("*C") == 1
+    assert count_non_dummy_atoms("*C(C)C") == 3
+
+
+def test_build_position_diversity_table_combines_frequency_and_structure_metrics() -> None:
+    dataframe = pd.DataFrame(
+        [
+            {"cleavage_position": 3, "fragment_smiles_plain": "*C"},
+            {"cleavage_position": 3, "fragment_smiles_plain": "*CC"},
+            {"cleavage_position": 3, "fragment_smiles_plain": "*CC"},
+            {"cleavage_position": 3, "fragment_smiles_plain": "*O"},
+            {"cleavage_position": 4, "fragment_smiles_plain": "*C"},
+        ]
+    )
+
+    summary = build_position_diversity_table(dataframe).set_index("cleavage_position")
+
+    assert summary.loc[3, "total_fragments"] == 4
+    assert summary.loc[3, "unique_fragments"] == 3
+    assert summary.loc[3, "normalized_unique_ratio"] == pytest.approx(0.75)
+    assert summary.loc[3, "shannon_entropy"] > 0.0
+    assert summary.loc[3, "normalized_shannon_entropy"] > 0.0
+    assert summary.loc[3, "mean_pairwise_tanimoto_distance"] > 0.0
+
+    assert summary.loc[4, "total_fragments"] == 1
+    assert summary.loc[4, "unique_fragments"] == 1
+    assert summary.loc[4, "mean_pairwise_tanimoto_distance"] == 0.0