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/PdfAttachmentClient.cs

@@ -14,7 +14,7 @@ public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentCli
     : BaseDocumentClient(httpClient, logger), IPdfAttachmentClient
 {
     /// <inheritdoc />
-    public async Task<AttachmentCheckResult> CheckAttachmentsAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    public async Task<AttachmentCheckResult> CheckAsync(Stream pdfStream, CancellationToken cancellationToken = default)
     {
         Logger.LogDebug("Checking PDF attachments from stream (multipart)");
 
@@ -28,7 +28,7 @@ public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentCli
     }
 
     /// <inheritdoc />
-    public async Task<AttachmentCheckResult> CheckAttachmentsAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    public async Task<AttachmentCheckResult> CheckAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
     {
         Logger.LogDebug("Checking PDF attachments from byte array (Base64 JSON)");
 
@@ -43,7 +43,7 @@ public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentCli
     }
 
     /// <inheritdoc />
-    public async Task<Dictionary<string, Stream>> ExtractAttachmentsAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    public async Task<Dictionary<string, Stream>> ExtractAsync(Stream pdfStream, CancellationToken cancellationToken = default)
     {
         Logger.LogDebug("Extracting PDF attachments from stream (multipart)");
 
@@ -57,7 +57,7 @@ public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentCli
     }
 
     /// <inheritdoc />
-    public async Task<Dictionary<string, Stream>> ExtractAttachmentsAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    public async Task<Dictionary<string, Stream>> ExtractAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
     {
         Logger.LogDebug("Extracting PDF attachments from byte array (Base64 JSON)");
 
@@ -73,7 +73,7 @@ public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentCli
 
     /// <inheritdoc />
     [Obsolete("API endpoint not implemented yet")]
-    public Task<Stream> AddAttachmentsAsync(Stream pdfStream, List<AttachmentRequestDto> attachments, CancellationToken cancellationToken = default)
+    public Task<Stream> AddAsync(Stream pdfStream, List<AttachmentRequestDto> attachments, CancellationToken cancellationToken = default)
     {
         Logger.LogWarning("AddAttachments endpoint is not implemented yet in API");
         throw new NotImplementedException("API endpoint /api/pdf/attachments/add is not implemented yet");
@@ -81,7 +81,7 @@ public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentCli
 
     /// <inheritdoc />
     [Obsolete("API endpoint not implemented yet")]
-    public Task<Stream> AddAttachmentsAsync(byte[] pdfBytes, List<AttachmentRequestDto> attachments, CancellationToken cancellationToken = default)
+    public Task<Stream> AddAsync(byte[] pdfBytes, List<AttachmentRequestDto> attachments, CancellationToken cancellationToken = default)
     {
         Logger.LogWarning("AddAttachments endpoint is not implemented yet in API");
         throw new NotImplementedException("API endpoint /api/pdf/attachments/add is not implemented yet");