added support for simultan downloads in files and talk, support for background downloads, enhanced loading in files with retry

lib/utils/downloads/download_job.dart

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+import 'package:flutter/foundation.dart';
+
+import '../../share_intent/remote_file_ref.dart';
+
+/// Snapshot of a single download's lifecycle. UI widgets rebuild whenever the
+/// owning [DownloadJob.status] notifier emits a new instance.
+sealed class DownloadStatus {
+  const DownloadStatus();
+}
+
+class DownloadInProgress extends DownloadStatus {
+  const DownloadInProgress(this.percent);
+
+  /// 0–100, or a value `<= 0` while the total size is still unknown
+  /// (indeterminate progress).
+  final double percent;
+}
+
+class DownloadDone extends DownloadStatus {
+  const DownloadDone(this.localPath);
+  final String localPath;
+}
+
+class DownloadCancelled extends DownloadStatus {
+  const DownloadCancelled();
+}
+
+class DownloadFailed extends DownloadStatus {
+  const DownloadFailed(this.message);
+  final String message;
+}
+
+/// Tracks a single in-flight or finished download. Survives widget dispose so
+/// that re-entering a screen (or opening the downloads overview) reattaches to
+/// the same job. Kept engine-agnostic on purpose — the native
+/// `background_downloader` task lives entirely inside [DownloadManager].
+class DownloadJob {
+  DownloadJob({
+    required this.remotePath,
+    required this.name,
+    this.remoteFile,
+  });
+
+  final String remotePath;
+  final String name;
+
+  /// Server-side reference so the viewer can offer "An Chat senden" /
+  /// "In Cloud speichern" for downloads triggered from Files or Talk.
+  final RemoteFileRef? remoteFile;
+
+  /// Native task id, set by [DownloadManager] once the task is enqueued.
+  String? taskId;
+
+  /// True once the finished file has been opened (auto-open or from the
+  /// overview). Opened jobs drop out of the downloads tray.
+  bool opened = false;
+
+  final ValueNotifier<DownloadStatus> status = ValueNotifier(
+    const DownloadInProgress(0),
+  );
+
+  bool get isFinished =>
+      status.value is DownloadDone ||
+      status.value is DownloadFailed ||
+      status.value is DownloadCancelled;
+
+  bool get isDone => status.value is DownloadDone;
+  bool get isFailed => status.value is DownloadFailed;
+  bool get isCancelled => status.value is DownloadCancelled;
+
+  /// Local file path once finished, else null.
+  String? get localPath {
+    final value = status.value;
+    return value is DownloadDone ? value.localPath : null;
+  }
+
+  void dispose() => status.dispose();
+}