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/ABSClient.swift

@@ -106,6 +106,10 @@ final class ABSClient {
         )
         item.mediaType = mediaType
         item.description = meta?.description
+        item.chapters = (raw.media?.chapters ?? []).compactMap { c in
+            guard let id = c.id, let start = c.start, let end = c.end, let title = c.title else { return nil }
+            return Chapter(id: id, start: start, end: end, title: title)
+        }
         return item
     }
 
@@ -225,4 +229,43 @@ final class ABSClient {
     }
 
     var bearerHeader: [String: String] { ["Authorization": "Bearer \(auth.token)"] }
+
+    // MARK: - Bookmarks
+
+    func fetchBookmarks(itemId: String, episodeId: String? = nil) async throws -> [ServerBookmark] {
+        let req = try makeRequest(path: progressPath(itemId: itemId, episodeId: episodeId))
+        let (data, response) = try await session.data(for: req)
+        guard let http = response as? HTTPURLResponse else { return [] }
+        if http.statusCode == 404 { return [] }
+        guard (200..<300).contains(http.statusCode) else { throw ABSClientError.httpStatus(http.statusCode) }
+        let dto = try JSONDecoder().decode(ProgressResponseDTO.self, from: data)
+        return (dto.bookmarks ?? []).compactMap { b in
+            guard let title = b.title, let time = b.time else { return nil }
+            return ServerBookmark(title: title, time: time, createdAt: b.createdAt)
+        }
+    }
+
+    func createBookmark(itemId: String, time: Double, title: String) async throws {
+        let body = try JSONSerialization.data(withJSONObject: ["title": title, "time": time])
+        let req = try makeRequest(path: "/api/me/item/\(itemId)/bookmark", method: "POST", body: body)
+        let (_, response) = try await session.data(for: req)
+        guard let http = response as? HTTPURLResponse, (200..<300).contains(http.statusCode) else {
+            throw ABSClientError.httpStatus((response as? HTTPURLResponse)?.statusCode ?? 0)
+        }
+    }
+
+    func deleteBookmark(itemId: String, time: Double) async throws {
+        let timeInt = Int(time)
+        let req = try makeRequest(path: "/api/me/item/\(itemId)/bookmark/\(timeInt)", method: "DELETE")
+        let (_, response) = try await session.data(for: req)
+        guard let http = response as? HTTPURLResponse, (200..<300).contains(http.statusCode) else {
+            throw ABSClientError.httpStatus((response as? HTTPURLResponse)?.statusCode ?? 0)
+        }
+    }
+}
+
+struct ServerBookmark {
+    let title: String
+    let time: Double
+    let createdAt: Double?
 }