chore: rework number and date inputs

[timakro]

This PR restyles the number and date inputs and adds error handling:

Due to the error handling this PR closes #264 and closes #159 and closes #307.

I don't think stacking the date inputs as suggested in #265 is a good idea. This PR removes the "from" and "to" texts so it might be a little bit less wide than before.

I also added optional units to the numer inputs as I figured we might need them at some point.

Things that are still to do:

• Translate custom error messages
• Decide if we want to put styles inside the components .svelte files
• Decide if we want to use the circular buttons for all catalogue items

[patrickskowronekdkfz]

Here are my thoughts on the changes:

1. I like the addition of the number input type—it makes it clearer to the user what should be entered. However, I’d prefer placing it only at the end, maybe something like .

Since we are size-constrained, I’d always aim to keep it as compact as possible.

2. I prefer the plus button over the arrow. I’d suggest using it for all inputs.

3. Removing the 'from' and 'to' text is a good improvement. Similar to point 1, I’d group all min/max inputs into one bracket, as it saves a lot of space. I tried stacking them but couldn’t make it work. We can probably close [Feature]: Make Dateinput stacked instead of side by side #265—I measured the sizes, and we reduced the width by about 100px, which looks much better.

4. I think providing feedback when a user enters an invalid value is a great idea. The error messages should be translated and improved for better clarity.

5. Regarding styling, I prefer keeping it within the component, as discussed. However, does it make sense to place it at the bottom part? Is there a standard from svelte where to put the html, script and style part. I think we should maintain a consistent order across all files.