server: update account confirmation email

[zven]

New design can be found here: https://www.figma.com/file/rq5IOcBWjVAl7tmvtq0GqS/Use-Cases?type=design&node-id=2887-6645&mode=design&t=8QD6fG8uLVLR16Kb-4

In case you need some input / graphics please get in touch with @Annicelia

[umut0]

@Annicelia We currently have the following footer for Emails:

Do we really want to delete that one and replace it with just the link?

Also i think it is good practice to provide the link for copying. Currently the email would look like this:

[Annicelia]

Hey @umut0, thank you, you are welcome to leave the link as it is. Copy: Could you please adopt the comma after "Account" and change the capital D to "d" (...deinen Account, um Badges...) Button: Could you please round the corners Footer: can you make it look like this? :)

[jona159]

Done in #111