task 8: add readingMode field to StoredBook, default to scroll

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

VorleserKit/Sources/Storage/StoredBook.swift

@@ -11,6 +11,7 @@ public class StoredBook {
 	public var lastPosition: Int
 	public var lastRead: Date?
 	public var voiceName: String?
+	public var readingMode: String?
 
 	public init(
 		bookID: UUID = UUID(),
@@ -20,7 +21,8 @@ public class StoredBook {
 		dateAdded: Date = .now,
 		lastPosition: Int = 0,
 		lastRead: Date? = nil,
-		voiceName: String? = nil
+		voiceName: String? = nil,
+		readingMode: String? = "scroll"
 	) {
 		self.bookID = bookID
 		self.title = title
@@ -30,5 +32,6 @@ public class StoredBook {
 		self.lastPosition = lastPosition
 		self.lastRead = lastRead
 		self.voiceName = voiceName
+		self.readingMode = readingMode
 	}
 }