Enhance workflow handling and enforce stricter exceptions

Enhanced `GetWorkflowsQueryHandler` to validate listing data
in workflow sources and return appropriate responses. Updated
`DocumentRepository.GetAsync` and `WorkflowRepository.CloseAsync`
to throw `NotSupportedException` for unimplemented functionality,
ensuring these methods cannot be used until finalized. Added
`DigitalData.TaskFlow.Domain.Enums` dependency to support new
logic in `GetWorkflowsQueryHandler`.

src/infrastructure/DigitalData.TaskFlow.Infrastructure/Repositories/DocumentRepository.cs

@@ -16,12 +16,7 @@ public sealed class DocumentRepository : IDocumentRepository
     /// <returns>Binary document payload.</returns>
     public Task<DocumentBinaryResult> GetAsync(string id, CancellationToken cancellationToken)
     {
-        return Task.FromResult(new DocumentBinaryResult
-        {
-            Content = [],
-            ContentType = "application/octet-stream",
-            FileName = $"{id}.bin",
-            Length = 0
-        });
+        throw new NotSupportedException(
+            "Document retrieval source (DB/DMS) is not finalized yet. Configure final integration before enabling GetAsync.");
     }
 }

src/infrastructure/DigitalData.TaskFlow.Infrastructure/Repositories/WorkflowRepository.cs

@@ -94,10 +94,7 @@ public sealed class WorkflowRepository(TaskFlowDbContext dbContext) : IWorkflowR
         CloseWorkflowDecision decision,
         CancellationToken cancellationToken)
     {
-        return Task.FromResult(new CloseWorkflowResult
-        {
-            ProcessId = processId,
-            IsClosed = true
-        });
+        throw new NotSupportedException(
+            "Closing write procedure is not finalized yet. Configure final DB procedure mapping before enabling CloseAsync.");
     }
 }