Song page behaviours

Some behaviours in the Songs page should be changed:

- After updating a song from the form and arriving at the song page, the back button in the browser should take you back to the search page. Currently, it takes you back to the form page. (This can be done by changing the `router.push` to a `router.back`.)
- After updating a song from the form and arriving at the song page, the song text (and author and melody) should be updated. Currently, it is not.

从 Songs page 更新流程开始，检查提交表单后使用的导航，包括 issue 中提到的 router.push。确认使用浏览器的后退按钮返回时会到达搜索页面，并且歌曲页面上显示的歌词、作者和旋律反映了此次更新。

由索引模型根据 Issue 内容生成。