refactor(workflow-engine): simplify paginated query with early-return on empty count

EF Core strips Include() for aggregate queries, so the count is already
lightweight. Add early return when totalCount is 0 to skip the data query
entirely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: danielskovli

src/Runtime/workflow-engine/src/WorkflowEngine.Data/Repository/EngineRepository.Reads.cs

@@ -555,8 +555,15 @@ await ExecuteWithRetry(
                 labelFilter: labelFilters
             );
 
+            // EF Core strips Include() for aggregate queries, so this is a lightweight count
             var totalCount = await baseQuery.CountAsync(cancellationToken);
 
+            if (totalCount == 0)
+            {
+                logger.SuccessfullyFetchedWorkflows(0);
+                return ([], 0);
+            }
+
             var workflows = await baseQuery
                 .OrderBy(wf => wf.CreatedAt)
                 .Skip((page - 1) * pageSize)