Form in 'timeline/' should not allow refreshing and send the request again

[eapl-gemugami]

In timeline/ we have a form to create a new twt.

When we press the Post button it's sending a Post request and loads the same page afterwards, so when we press the refresh button in your browser (in my case it was accidentally) you get the following message:

And then the browser shows the following text:

Document Expired
This document is no longer available.

Finally the .txt file stores the same twt each time the page is refreshed.

2024-12-13T21:35:37Z	A test!
2024-12-13T21:37:05Z	A test!
2024-12-13T21:39:32Z	A test!

To solve this issue, the pattern Post-Redirect-Get could be used:
https://en.wikipedia.org/wiki/Post/Redirect/Get

[sorenpeter]

Yes, it has also been annoying me when this happens.

It looks like one of us already tried to fix this back in the day:
https://github.com/sorenpeter/timeline/blob/main/views/new_twt.php#L83