clearer success message

[tttp]

Hi,

on the share step, we are already clearly indicating if the supporter needs to check their inbox (for double opt-in). However, a "normal" signatory doesn't have a clear confirmation, beside having the share.intro thanking.

we should:

1. remove the "Great, you’ve signed 👍." from all the share.intro
2. modify the thank you text to return {t("Thank you")};

• a new text share.confirmed = "Great, your action is recorded 👍." and display it with the thank you

3. may be display longer? or never close even?