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/Views/LibraryGridView.swift

@@ -3,6 +3,7 @@ import SwiftUI
 struct LibraryGridView: View {
     let items: [LibraryItem]
     var onRefresh: (() async -> Void)? = nil
+    var dimDownloading: Bool = false
     var onSelect: (LibraryItem) -> Void
 
     @AppStorage("libraryCoverSize") private var coverSize: Double = Self.defaultCoverSize
@@ -22,7 +23,7 @@ struct LibraryGridView: View {
         ScrollView {
             LazyVGrid(columns: gridColumns, spacing: gridSpacing) {
                 ForEach(items) { item in
-                    LibraryItemCell(item: item)
+                    LibraryItemCell(item: item, dimDownloading: dimDownloading)
                         .onTapGesture { onSelect(item) }
                 }
             }