Lack of encoding in RSS support

Hello,

The RSS URL of blog seems to not render accented characters.

I suppose it's because of the response header "Content-Type: text/xml" without charset (utf8).

URL to reproduce : https://niji.tech/rss.xml

A french user using a RSS client reported the problem to me today.

Thx

先開啟 https://niji.tech/rss.xml，檢查其回應標頭以及重音字元的編碼方式。透過檢查法語 RSS 用戶端是否能正確呈現重音字元，並確認回應宣告了適當的 charset，來確認 fix。

由索引模型根據 Issue 內容生成。