Refactor: Rename DocumentOperator to DocumentService

Updated project and solution files to rename and restructure
`DocumentOperator` to `DocumentService`. Modified project
references in `DocumentService.API.csproj`, `DocumentService.Application.csproj`,
and `DocumentService.Infrastructure.csproj` to reflect the new
naming convention. Updated `DocumentService.sln` to remove
old project references, add new ones, and adjust configuration
and nested project mappings accordingly. This change aligns
the project structure with the new naming convention.

DocumentService.Application/Common/Interfaces/ISwissQrCodeProcessor.cs

@@ -0,0 +1,32 @@
+using Codecrete.SwissQRBill.Generator;
+
+namespace DocumentService.Application.Common.Interfaces;
+
+/// <summary>
+/// Interface for Swiss QR Code processing operations.
+/// Extracts and parses Swiss QR Codes from PDF documents.
+/// </summary>
+public interface ISwissQrCodeProcessor
+{
+    /// <summary>
+    /// Extracts and parses Swiss QR Code from a PDF document.
+    /// Returns both parsed Bill object and raw QR text lines.
+    /// </summary>
+    /// <param name="pdfStream">
+    /// PDF document stream. Must be readable and positioned at the beginning (Position = 0).
+    /// Non-seekable streams are supported. Caller is responsible for disposal.
+    /// </param>
+    /// <param name="pageNumbers">Optional: Specific page numbers to scan (1-indexed). If null, scans all pages starting with last page.</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Tuple: (Parsed Codecrete Bill, Raw QR lines as string array)</returns>
+    /// <exception cref="Domain.Common.Exceptions.NotFoundException">
+    /// Thrown when no Swiss QR Code is found in the specified pages
+    /// </exception>
+    /// <exception cref="ArgumentException">
+    /// Thrown when stream is empty or (for seekable streams) not positioned at the beginning
+    /// </exception>
+    Task<(Bill Bill, string[] RawLines)> ExtractSwissQrCodeAsync(
+        Stream pdfStream, 
+        int[]? pageNumbers = null, 
+        CancellationToken cancellationToken = default);
+}