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.Client/Interfaces/IWorkflowsClient.cs

@@ -0,0 +1,59 @@
+using DocumentService.Application.Common.DTOs;
+
+namespace DocumentService.Client.Interfaces;
+
+/// <summary>
+/// Orchestrated multi-step workflows that combine multiple DocumentService operations into
+/// a single, higher-level call. Prefer these over manually chaining individual clients.
+/// </summary>
+public interface IWorkflowsClient
+{
+    /// <summary>
+    /// Validates the PDF and extracts its Swiss QR Code in a single call.
+    /// Validation runs first; extraction is only attempted on valid documents.
+    /// </summary>
+    /// <param name="pdfBytes">PDF file as byte array.</param>
+    /// <param name="raw">
+    /// <c>false</c> (default) – returns a parsed <see cref="SwissQrCodeExtractionResult.Bill"/> object.<br/>
+    /// <c>true</c> – returns raw QR text lines without parsing.
+    /// </param>
+    /// <param name="throwIfInvalid">
+    /// <c>true</c> (default) – throws <see cref="InvalidOperationException"/> when the PDF fails validation.<br/>
+    /// <c>false</c> – returns <c>null</c> instead, allowing the caller to handle the case without a try/catch.
+    /// </param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>
+    /// Swiss QR Code extraction result, or <c>null</c> if the document is invalid and
+    /// <paramref name="throwIfInvalid"/> is <c>false</c>.
+    /// </returns>
+    /// <exception cref="InvalidOperationException">
+    /// Thrown when the PDF fails validation and <paramref name="throwIfInvalid"/> is <c>true</c>.
+    /// </exception>
+    Task<SwissQrCodeExtractionResult?> ExtractSwissQrCodeValidatedAsync(
+        byte[] pdfBytes,
+        bool raw = false,
+        bool throwIfInvalid = true,
+        CancellationToken cancellationToken = default);
+
+    /// <inheritdoc cref="ExtractSwissQrCodeValidatedAsync(byte[], bool, bool, CancellationToken)"/>
+    /// <param name="pdfStream">PDF file as a stream.</param>
+    /// <param name="raw"><inheritdoc cref="ExtractSwissQrCodeValidatedAsync(byte[], bool, bool, CancellationToken)" path="/param[@name='raw']"/></param>
+    /// <param name="throwIfInvalid"><inheritdoc cref="ExtractSwissQrCodeValidatedAsync(byte[], bool, bool, CancellationToken)" path="/param[@name='throwIfInvalid']"/></param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    Task<SwissQrCodeExtractionResult?> ExtractSwissQrCodeValidatedAsync(
+        Stream pdfStream,
+        bool raw = false,
+        bool throwIfInvalid = true,
+        CancellationToken cancellationToken = default);
+
+    /// <inheritdoc cref="ExtractSwissQrCodeValidatedAsync(byte[], bool, bool, CancellationToken)"/>
+    /// <param name="filePath">Absolute or relative path to the PDF file.</param>
+    /// <param name="raw"><inheritdoc cref="ExtractSwissQrCodeValidatedAsync(byte[], bool, bool, CancellationToken)" path="/param[@name='raw']"/></param>
+    /// <param name="throwIfInvalid"><inheritdoc cref="ExtractSwissQrCodeValidatedAsync(byte[], bool, bool, CancellationToken)" path="/param[@name='throwIfInvalid']"/></param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    Task<SwissQrCodeExtractionResult?> ExtractSwissQrCodeValidatedAsync(
+        string filePath,
+        bool raw = false,
+        bool throwIfInvalid = true,
+        CancellationToken cancellationToken = default);
+}