chore: Remove obsolete Domain enums (DocumentOperationType, ProcessingStatus)

- These enums were part of initial scaffolding but never used
- Domain layer cleanup - removing unused code

DocumentOperator.Domain/Models/Enums/DocumentOperationType.cs

@@ -1,10 +0,0 @@
-namespace DocumentOperator.Domain.Models.Enums;
-
-public enum DocumentOperationType
-{
-    Validate,
-    ExtractAttachments,
-    Concatenate,
-    ApplyStamp,
-    EmbedCertificate
-}

DocumentOperator.Domain/Models/Enums/ProcessingStatus.cs

@@ -1,9 +0,0 @@
-namespace DocumentOperator.Domain.Models.Enums;
-
-public enum ProcessingStatus
-{
-    Pending,
-    Processing,
-    Success,
-    Failed
-}