fix: 末尾频道快照 + h-skip 累加 + 清理死代码

- 补 download_all_chat 末尾 snapshot + reset，修复最后频道永远卡「🚀下载中」
- h-skip 改为跨频道累加，解决切频道视觉归零
- 清理前端 currentFilter 死变量 / download_stat 无意义三元

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

module/download_stat.py

@@ -236,9 +236,8 @@ def clear_skipped_message(chat_id: str, message_id: int):
 
 def remove_download_entry(chat_id, message_id):
     """从下载结果中移除条目，使其不再显示在正在下载列表"""
-    chat_key = chat_id if not isinstance(chat_id, str) else chat_id
-    if chat_key in _download_result and message_id in _download_result[chat_key]:
-        del _download_result[chat_key][message_id]
+    if chat_id in _download_result and message_id in _download_result[chat_id]:
+        del _download_result[chat_id][message_id]
 
 
 async def update_download_status(