Fix SAS point classification stats for explicit-site datasets and improve cluster logging

- PocketRescorer: fall back to explicit site residue atoms for point
  labeling when no ligand atoms are available, fixing 0-positives in
  binary classification stats for site-based eval-predict
- SLinkClustererV2: log cluster count and sizes instead of full contents

src/main/groovy/cz/siret/prank/geom/clustering/SLinkClustererV2.java

@@ -74,7 +74,7 @@ public class SLinkClustererV2<E> implements Clusterer<E> {
 
         List<List<E>> result = new ArrayList<>(clusterMap.values());
 
-        log.info("clusters: {}", result);
+        log.info("clusters ({}): sizes {}", result.size(), result.stream().map(List::size).toList());
         log.info("clusters together: {} / {}", result.stream().mapToInt(List::size).sum(), elements.size());
 
         return result;

src/main/groovy/cz/siret/prank/prediction/pockets/rescorers/PocketRescorer.groovy

@@ -26,6 +26,11 @@ abstract class PocketRescorer implements Parametrized {
         this.ligandedProtein = liganatedProtein
         if (liganatedProtein != null) {
             ligandAtoms = liganatedProtein.allRelevantLigandAtoms
+            // Fallback: use explicit site residue atoms for point labeling
+            if ((ligandAtoms == null || ligandAtoms.empty) && !liganatedProtein.sites.isEmpty()) {
+                List<Atoms> siteAtomsList = liganatedProtein.sites.collect { it.atoms }
+                ligandAtoms = Atoms.union(siteAtomsList)
+            }
         }
     }