refactor: address PR review comments for ingestion workflow

src/NexusReader.Application/Abstractions/Services/IBookStorageService.cs

@@ -1,7 +1,29 @@
 namespace NexusReader.Application.Abstractions.Services;
 
+/// <summary>
+/// Service for managing ebook and cover file storage.
+/// </summary>
 public interface IBookStorageService
 {
+    /// <summary>
+    /// Saves an ebook file and returns its relative path/URL.
+    /// </summary>
     Task<string> SaveEbookAsync(byte[] data, string fileName);
+
+    /// <summary>
+    /// Saves an ebook file using a stream and returns its relative path/URL.
+    /// </summary>
+    Task<string> SaveEbookAsync(Stream data, string fileName);
+
+    /// <summary>
+    /// Saves a cover image and returns its relative path/URL. 
+    /// Returns null if no cover data is provided.
+    /// </summary>
     Task<string?> SaveCoverAsync(byte[] data, string fileName);
+
+    /// <summary>
+    /// Saves a cover image using a stream and returns its relative path/URL.
+    /// Returns null if no cover data is provided.
+    /// </summary>
+    Task<string?> SaveCoverAsync(Stream data, string fileName);
 }