feat: 增加 systemd 定时执行与断点续跑

- backend/server.py: 信令 WebSocket 被远端关闭或视频流停滞超过阈值时自动拆除会话，
  由 finally 释放网易云端实例，避免会话空挂、后续 /start 一直拿到 503
- bin/maa-online-daily-run: 新增日常任务包装脚本，等待 API 就绪、启动云游戏、
  停滞看门狗（连续 ScreencapFailed 或 Disconnected）、失败即释放云会话并最多重试 3 次
- bin/maa-resume-tasks.py: 新增断点续跑规划器，重试时只运行未出现 Completed 的任务，
  全部完成则直接判定成功，不再开启新会话；StartUp 永不跳过
- systemd/: 新增 server/daily/update 服务与定时器模板，每天 04:00 起随机 0-2 小时执行
- bin/maa-online-install-systemd: 渲染 __ROOT__ 并安装、启用上述单元
- README.md, user_config/README.md: 补充自动定时执行、断点续跑与已知限制说明
- .gitignore: 忽略生成的 config/tasks/daily-resume.toml

systemd/maa-daily.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=MAA Online daily task (Arknights via NetEase cloud game)
+Requires=maa-online-server.service
+After=maa-online-server.service
+
+[Service]
+Type=oneshot
+ExecStart=__ROOT__/bin/maa-online-daily-run
+# A normal run takes about 25 minutes; the runner's own per-attempt watchdog
+# aborts a hung session well before this ceiling.
+TimeoutStartSec=7200
+# Safety net: whatever stops the unit (success, failure, timeout), make sure
+# the remote cloud session is released.
+ExecStopPost=/bin/sh -c "/usr/bin/curl --noproxy '*' -fsS -X POST http://127.0.0.1:22888/exit || true"

systemd/maa-daily.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Run MAA Online daily at a random moment between 04:00 and 06:00
+
+[Timer]
+OnCalendar=*-*-* 04:00:00
+RandomizedDelaySec=2h
+Persistent=true
+Unit=maa-daily.service
+
+[Install]
+WantedBy=timers.target

systemd/maa-online-server.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=MAA Online cloud game API server
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=__ROOT__/bin/maa-online-server
+Restart=always
+RestartSec=5
+# Belt and braces: never let a proxy environment leak into the cloud gaming
+# server (bin/maa-online-server already unsets these).
+Environment=NO_PROXY=localhost,127.0.0.1,::1
+
+[Install]
+WantedBy=multi-user.target

systemd/maa-update.service

@@ -0,0 +1,7 @@
+[Unit]
+Description=Weekly MAA Online maintenance (maa-cli, MaaCore and resource updates)
+
+[Service]
+Type=oneshot
+ExecStart=__ROOT__/bin/maa-online-update
+TimeoutStartSec=1800

systemd/maa-update.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Weekly MAA Online maintenance, Sunday 03:20 (before the daily window)
+
+[Timer]
+OnCalendar=Sun *-*-* 03:20:00
+RandomizedDelaySec=30m
+Persistent=true
+Unit=maa-update.service
+
+[Install]
+WantedBy=timers.target