feat(douyu): 兑换成功后生成结果图片并自动复制到剪贴板

- 账号表格新增兑换图片列，展示每账号最近兑换成功的结果卡片
- 新完成兑换任务自动生成图片并复制到剪贴板（批量时最后完成者覆盖）
- canvas 绘制兑换卡片：商品图/商品名/游戏角色/区服/兑换账号/时间
- 后端兑换成功结果补充 game_name/game_channel/account_name 字段
- 不支持剪贴板的环境降级为点击查看大图

web/backend/services/douyu_runner.py

@@ -1835,7 +1835,13 @@ class DouyuBatchRunner:
             task,
             "success",
             f"兑换成功: {(goods.name if goods else '') or commodity_id}",
-            {"goods": goods.raw if goods else None, **result},
+            {
+                "goods": goods.raw if goods else None,
+                "game_name": account.game_name or "",
+                "game_channel": account.game_channel or "",
+                "account_name": account.nickname or account.username or account.uid or f"#{account.id}",
+                **result,
+            },
         )
 
     def _execute_exchange_esports_goods(
@@ -1901,6 +1907,9 @@ class DouyuBatchRunner:
             message += f" x{quantity}"
         if account.esports_points is not None:
             message += f"，电竞积分: {account.esports_points}"
+        result["game_name"] = account.esports_game_name or ""
+        result["game_channel"] = account.esports_game_channel or ""
+        result["account_name"] = account.nickname or account.username or account.uid or f"#{account.id}"
         self._mark_task(db, task, "success", message, result)
 
     def _execute_query_game_name(self, db: Session, task: DouyuTask, account: Account, cookie: str, config: dict):