Add WorkflowsClient for PDF validation and QR extraction

Introduced a new `WorkflowsClient` to orchestrate multi-step
operations, combining `IPdfValidationClient` and
`ISwissQrCodeClient`. Added methods to validate PDFs and extract
Swiss QR Codes in a single call, with overloads for byte arrays,
streams, and file paths. Registered `WorkflowsClient` as a scoped
service in `ServiceCollectionExtensions`.

Updated `PdfValidationResult` with an `IsValid` property to
simplify PDF validity checks. Added `IWorkflowsClient` interface
to define the contract for the new client, with detailed XML
documentation for its methods.

DocumentService.Application/Common/DTOs/PdfValidationResult.cs

@@ -17,4 +17,7 @@ public record PdfValidationResult(
     string PdfVersion,
     bool HasAttachments,
     int AttachmentCount,
-    bool IsEncrypted);
+    bool IsEncrypted)
+{
+    public bool IsValid => !IsEncrypted && PageCount > 0 && FileSizeBytes > 0;
+}