Refactor: Standardize method names across clients

Renamed methods across multiple client classes for consistency,
shortening and aligning naming conventions (e.g., `CheckAttachmentsAsync` → `CheckAsync`, `ValidatePdfAsync` → `ValidateAsync`).

Updated corresponding interfaces, unit tests, and documentation
to reflect the new method names. Standardized method signatures
to support both `Stream` and `byte[]` overloads consistently.

Improved error handling in tests and updated examples in the
README for batch processing and validation scenarios. Enhanced
API endpoint overview for clarity.

DocumentService.Client/Clients/ZugferdClient.cs

@@ -13,7 +13,7 @@ namespace DocumentService.Client.Clients;
 public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger) : BaseDocumentClient(httpClient, logger), IZugferdClient
 {
     /// <inheritdoc />
-    public async Task<ZugferdCheckResult> HasZugferdAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    public async Task<ZugferdCheckResult> CheckAsync(Stream pdfStream, CancellationToken cancellationToken = default)
     {
         var result = await SendMultipartAsync<ZugferdCheckResult>(
             "/api/pdf/zugferd/has-zugferd",
@@ -25,7 +25,7 @@ public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger)
     }
 
     /// <inheritdoc />
-    public async Task<ZugferdCheckResult> HasZugferdAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    public async Task<ZugferdCheckResult> CheckAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
     {
         var request = new HasZugferdRequest { Base64Pdf = ToBase64(pdfBytes) };
 
@@ -38,7 +38,7 @@ public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger)
     }
 
     /// <inheritdoc />
-    public async Task<Stream> ExtractZugferdAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    public async Task<Stream> ExtractAsync(Stream pdfStream, CancellationToken cancellationToken = default)
     {
         // asFile=true returns the XML file directly (application/xml stream)
         return await SendMultipartForStreamAsync(
@@ -49,7 +49,7 @@ public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger)
     }
 
     /// <inheritdoc />
-    public async Task<Stream> ExtractZugferdAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    public async Task<Stream> ExtractAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
     {
         var request = new ExtractZugferdRequest { Base64Pdf = ToBase64(pdfBytes) };
 
@@ -61,7 +61,7 @@ public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger)
     }
 
     /// <inheritdoc />
-    public async Task<ZugferdExtractionResult> ExtractZugferdAsResultAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    public async Task<ZugferdExtractionResult> ExtractAsResultAsync(Stream pdfStream, CancellationToken cancellationToken = default)
     {
         // asFile=false returns JSON with metadata + XML content
         var result = await SendMultipartAsync<ZugferdExtractionResult>(
@@ -74,7 +74,7 @@ public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger)
     }
 
     /// <inheritdoc />
-    public async Task<ZugferdExtractionResult> ExtractZugferdAsResultAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    public async Task<ZugferdExtractionResult> ExtractAsResultAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
     {
         var request = new ExtractZugferdRequest { Base64Pdf = ToBase64(pdfBytes) };