Add whereNotNull to count query sort-field EXISTS

The list CTE's INNER JOIN on search already excludes entities whose
sort-field value is NULL (truncated long values stored as NULL by
buildEntitySearch). Add the same whereNotNull to the count query's
EXISTS so totalItems matches the reachable set. Matters for fields
like metadata.description where ~128K entities have NULL values.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Fredrik Adelöw <freben@gmail.com>

plugins/catalog-backend/src/service/DefaultEntitiesCatalog.ts

@@ -505,7 +505,8 @@ export class DefaultEntitiesCatalog implements EntitiesCatalog {
           this.database('search')
             .select(this.database.raw(1))
             .whereRaw('search.entity_id = final_entities.entity_id')
-            .where('search.key', sortField.field),
+            .where('search.key', sortField.field)
+            .whereNotNull('search.value'),
         );
       }