feat(jm): 新增 JM 漫画下载打包服务（9004，移植自 qqbot jm 模块）

- source/jm/jm.py：aiohttp + jmcomic，GET /jm/get_comic?id=xxx[&range=起-止]
  下载至 cache/jm 隐藏暂存目录 → webp 转 jpg 打包 ZIP → HTTP 直返 → 600s 延时删除
  单次上限 30 章；per-album 锁防并发；cache_sweep 兜底清理；/jm/cache_info 运维接口
- source/main.py：聚合层注册 /jm/get_comic（新增 JM_BACKEND，复用 proxy()）
- systemd/jm.service：独立系统服务（Restart=always，日志 /var/log/jm.log）
- README / 部署与运维文档同步更新

systemd/jm.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=JM Comic Download API Service
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Environment=PATH=/home/openapi/env/general/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+Type=simple
+WorkingDirectory=/home/openapi/source/jm
+ExecStart=/home/openapi/env/general/bin/python /home/openapi/source/jm/jm.py
+Restart=always
+RestartSec=5
+StandardOutput=append:/var/log/jm.log
+StandardError=append:/var/log/jm.log
+
+[Install]
+WantedBy=multi-user.target