[Bug] Fix Docker build/runtime issues on Windows checkouts

[Sylthionys]

Summary

Fix Docker build/runtime issues that appear when building RSSBox from a Windows checkout.

What Changed

• normalize scripts/entrypoint.sh to LF during Docker build to avoid CRLF-related startup failures
• stop installing /etc/cron.d/rt_cron via crontab, since files under /etc/cron.d already use system-cron format with username fields
• change the hourly cron expression from */60 to 0 * * * * for clearer, more portable behavior

Problem

When building from a Windows checkout, the container could fail to start because entrypoint.sh was copied with CRLF line endings. This caused errors such as:

• exec /usr/local/bin/entrypoint.sh: no such file or directory
• broken shell parsing due to \r line endings

In addition, the Docker build attempted to install /etc/cron.d/rt_cron with crontab, even though the file uses /etc/cron.d system-cron format with a username field.

Verification

Verified locally by rebuilding and starting the Docker-based test instance successfully after these changes.

[versun]

补了一个 follow-up commit（78fd48f），把 config/rt_cron 的 CRLF 归一化也补上了，并新增了 .gitattributes 来固定这些关键文件使用 LF checkout。这样 Windows checkout 下的 cron 配置也能和 entrypoint 一样稳定工作。

感谢PR贡献