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/Services/BookmarkManager.swift

@@ -0,0 +1,86 @@
+import Foundation
+import Observation
+
+struct Bookmark: Codable, Identifiable {
+    let id: UUID
+    let createdAt: Date
+    let itemId: String
+    let episodeId: String?
+    let itemTitle: String
+    var title: String
+    let chapterTitle: String?
+    let time: Double
+}
+
+@Observable
+@MainActor
+final class BookmarkManager {
+    private(set) var bookmarks: [Bookmark] = []
+
+    private var saveFile: URL {
+        AppPaths.supportDirectory.appendingPathComponent("bookmarks.json")
+    }
+
+    init() { load() }
+
+    func add(item: LibraryItem, time: Double, title: String, chapters: [Chapter]) {
+        let chapter = chapters.last { $0.start <= time }
+        let bm = Bookmark(
+            id: UUID(),
+            createdAt: Date(),
+            itemId: item.id,
+            episodeId: item.episodeId,
+            itemTitle: item.title,
+            title: title,
+            chapterTitle: chapter?.title,
+            time: time
+        )
+        bookmarks.insert(bm, at: 0)
+        save()
+    }
+
+    func delete(_ bookmark: Bookmark) {
+        bookmarks.removeAll { $0.id == bookmark.id }
+        save()
+    }
+
+    func bookmarks(for item: LibraryItem) -> [Bookmark] {
+        bookmarks.filter { $0.itemId == item.id && $0.episodeId == item.episodeId }
+            .sorted { $0.time < $1.time }
+    }
+
+    /// Replaces bookmarks for an item with the server-loaded list (keeps bookmarks for other items).
+    func mergeFromServer(_ serverBookmarks: [ServerBookmark], for item: LibraryItem) {
+        bookmarks.removeAll { $0.itemId == item.id && $0.episodeId == item.episodeId }
+        let chapters = item.chapters
+        for sb in serverBookmarks {
+            let chapter = chapters.last { $0.start <= sb.time }
+            let bm = Bookmark(
+                id: UUID(),
+                createdAt: sb.createdAt.map { Date(timeIntervalSince1970: $0 / 1000) } ?? Date(),
+                itemId: item.id,
+                episodeId: item.episodeId,
+                itemTitle: item.title,
+                title: sb.title,
+                chapterTitle: chapter?.title,
+                time: sb.time
+            )
+            bookmarks.append(bm)
+        }
+        bookmarks.sort { $0.createdAt > $1.createdAt }
+        save()
+    }
+
+    private func save() {
+        try? FileManager.default.createDirectory(
+            at: AppPaths.supportDirectory, withIntermediateDirectories: true)
+        if let data = try? JSONEncoder().encode(bookmarks) {
+            try? data.write(to: saveFile)
+        }
+    }
+
+    private func load() {
+        guard let data = try? Data(contentsOf: saveFile) else { return }
+        bookmarks = (try? JSONDecoder().decode([Bookmark].self, from: data)) ?? []
+    }
+}