feat(flutter): 接入分类记录收藏与下载授权

lib/core/widgets/download_action.dart

@@ -0,0 +1,29 @@
+// Author: fruit.com.cn
+
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import '../../l10n/app_localizations.dart';
+import '../data/services/download_controller.dart';
+import 'auth_gate.dart';
+
+/// 详情页与播放页共用的下载授权入口。
+///
+/// 未登录先走登录闸；业务拒绝时直接展示后端 message。
+Future<void> requestEpisodeDownload(
+  BuildContext context,
+  String episodeId,
+) async {
+  if (!await ensureSignedIn(context)) return;
+  if (!context.mounted) return;
+  final result = await context.read<DownloadController>().grant(episodeId);
+  if (!context.mounted) return;
+  final l10n = AppLocalizations.of(context)!;
+  final hasBackendMessage = result.message?.trim().isNotEmpty ?? false;
+  final message = result.ok
+      ? l10n.downloadGranted
+      : hasBackendMessage
+      ? result.message!
+      : l10n.downloadGrantFailed;
+  ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(message)));
+}