Cleanup start of 2024

[flosse]

This project has grown slowly and with few resources, and the overall state can still be described as a prototype, but it is now being used productively, so some hygiene is needed. Before starting any major work, we should urgently clean up.
Here are a few important points that come to mind:

• Reduce the number of issue to less than 25
• Tidy up the error handling
• Look for TODO comments

And then we need some changes

• Migrate to axum #459 (or at least update to rocket v0.5.0)
• Tech stack for new frontend #448

[wellemut]

With our limited ressource, we have much more good ideas than we can complete. But closing all those good ideas, with a big ammount of resarch in it, does not help eather.

I am rather working with board. @flosse
Most important is the General Product Backlog https://github.com/orgs/kartevonmorgen/projects/1?fullscreen=true
There you should start your focus on the colum "Todo"