feat: implement background ebook indexing with progress tracking and real-time UI updates

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

@@ -0,0 +1,17 @@
+using FluentResults;
+
+namespace NexusReader.Application.Abstractions.Services;
+
+/// <summary>
+/// Service abstraction to extract raw text content from EPUB chapters.
+/// </summary>
+public interface IEpubExtractor
+{
+    /// <summary>
+    /// Extracts the sanitized, plain-text content of each chapter in the EPUB file.
+    /// </summary>
+    /// <param name="relativePath">The relative storage path of the EPUB file.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A list of plain-text chapters, or a failure result.</returns>
+    Task<Result<List<string>>> ExtractChaptersTextAsync(string relativePath, CancellationToken cancellationToken = default);
+}