Add workflow and document APIs, middleware, and Swagger

Introduced `CloseWorkflowRequest` for closing workflows.
Added `DocumentsController` for document downloads and
`WorkflowsController` for workflow retrieval and closing.

Implemented `ExceptionHandlingMiddleware` for global exception
handling with structured API responses.

Enhanced Swagger configuration with metadata and production
support. Added `Scalar.AspNetCore` for API reference mapping.

Updated project dependencies and improved API documentation.

src/presentation/DigitalData.TaskFlow.API/Contracts/Workflows/CloseWorkflowRequest.cs

@@ -0,0 +1,22 @@
+namespace DigitalData.TaskFlow.API.Contracts.Workflows;
+
+/// <summary>
+/// Represents the request payload for closing a workflow.
+/// </summary>
+public sealed class CloseWorkflowRequest
+{
+    /// <summary>
+    /// Gets or sets the selected closing method identifier.
+    /// </summary>
+    public required int ClosingMethodId { get; init; }
+
+    /// <summary>
+    /// Gets or sets an optional user comment.
+    /// </summary>
+    public string? Comment { get; init; }
+
+    /// <summary>
+    /// Gets or sets an optional rejection reason identifier.
+    /// </summary>
+    public int? RejectionReasonId { get; init; }
+}