Add new endpoint and improve exception handling

Removed the `asByte` parameter from XML documentation in `DocumentController.cs`, indicating the method no longer supports byte array returns. Added a new HTTP POST endpoint `CloseAsync` in `WorkflowsController.cs`, which is currently not implemented and throws a `NotImplementedException`. Enhanced `ExceptionHandlingMiddleware.cs` to handle `NotImplementedException` by logging a warning and returning a `501 Not Implemented` response in a problem details format.

src/presentation/DigitalData.TaskFlow.API/Controllers/DocumentController.cs

@@ -18,7 +18,6 @@ public sealed class DocumentController(ISender sender) : ControllerBase
     /// <param name="id">Document identifier.</param>
     /// <param name="userId">User identifier.</param>
     /// <param name="processId">Process identifier.</param>
-    /// <param name="asByte">Return document as byte array.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
     /// <returns>Document response envelope grouped by source.</returns>
     [HttpGet("{id:int}")]

src/presentation/DigitalData.TaskFlow.API/Controllers/WorkflowsController.cs

@@ -27,4 +27,20 @@ public sealed class WorkflowsController(ISender sender) : ControllerBase
     {
         return Ok(await sender.Send(new GetWorkflowsQuery(wisagId), cancellationToken));
     }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="wisagId"></param>
+    /// <param name="source"></param>
+    /// <param name="processId"></param>
+    /// <param name="cancellationToken"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    [HttpPost("{wisagId:int}/{source}/{processId:long}/closing")]
+    [ProducesResponseType(StatusCodes.Status501NotImplemented)]
+    public Task<ActionResult<JsonElement>> CloseAsync([FromRoute] int wisagId, [FromRoute] string source, [FromRoute] long processId, CancellationToken cancellationToken)
+    {
+        throw new NotImplementedException();
+    }
 }

src/presentation/DigitalData.TaskFlow.API/Middleware/ExceptionHandlingMiddleware.cs

@@ -63,6 +63,22 @@ public sealed class ExceptionHandlingMiddleware(RequestDelegate next, ILogger<Ex
             context.Response.ContentType = "application/problem+json";
             await context.Response.WriteAsync(JsonSerializer.Serialize(response, JsonOptions));
         }
+        catch (NotImplementedException ex)
+        {
+            logger.LogWarning(ex, "Not implemented: {Method} {Path}",
+                context.Request.Method, context.Request.Path);
+
+            var response = new
+            {
+                type   = "https://tools.ietf.org/html/rfc7807",
+                title  = "Not Implemented",
+                status = StatusCodes.Status501NotImplemented
+            };
+
+            context.Response.StatusCode  = StatusCodes.Status501NotImplemented;
+            context.Response.ContentType = "application/problem+json";
+            await context.Response.WriteAsync(JsonSerializer.Serialize(response, JsonOptions));
+        }
         catch (Exception ex)
         {
             logger.LogError(ex, "Unhandled exception for {Method} {Path}",