Add chapters, history, bookmarks, live download progress, and i18n

- Chapter navigation with auto-scroll to current chapter and end-of-chapter sleep timer
- Opt-in listening history (local-only) with XML export and per-item quick menu
- Bookmarks with server sync via Audiobookshelf API
- Live MB counter during downloads via URLSessionDownloadTask delegate
- In-progress downloads shown in "Heruntergeladen" with dimmed cover + ring overlay
- Cover image cache (50 MB memory / 500 MB disk URLCache)
- German/English localization (de.lproj, en.lproj)
- Loading spinner now triggers immediately on view switch instead of waiting for the network

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

ABS Client/Audiobookshelf swift/Models/APIResponses.swift

@@ -31,11 +31,19 @@ struct LibraryItemDTO: Decodable {
     let media: MediaDTO?
 }
 
+struct ChapterDTO: Decodable {
+    let id: Int?
+    let start: Double?
+    let end: Double?
+    let title: String?
+}
+
 struct MediaDTO: Decodable {
     let metadata: MetadataDTO?
     let duration: Double?
     let audioFiles: [AudioFileDTO]?
     let episodes: [EpisodeDTO]?
+    let chapters: [ChapterDTO]?
 }
 
 struct MetadataDTO: Decodable {
@@ -69,6 +77,12 @@ struct AudioFileDTO: Decodable {
     }
 }
 
+struct BookmarkDTO: Decodable {
+    let title: String?
+    let time: Double?
+    let createdAt: Double?
+}
+
 struct ProgressResponseDTO: Decodable {
     let id: String?
     let libraryItemId: String?
@@ -77,6 +91,7 @@ struct ProgressResponseDTO: Decodable {
     let duration: Double?
     let isFinished: Bool?
     let lastUpdate: Double?
+    let bookmarks: [BookmarkDTO]?
 }
 
 struct MeResponseDTO: Decodable {