Add German translations for Blanco Unit integration

[knuffifix]

Added German translations for exceptions, configuration, entities, and services in Blanco Unit integration.

[knuffifix]

Hi! I put together a German translation for the integration (translations/de.json), covering config flow, entities, and services.
I used Claude as a starting point for the translation and then reviewed it myself to make sure the wording fits Home Assistant's style and terminology (Kühltemperatur, Wasserhärte, etc.), and that all keys match en.json exactly.
Screenshot attached showing it working in Home Assistant. Happy to adjust wording if anything sounds off!

[vanilla-thunder]

could we possibly talk about the "Außer Betrieb" translation? The meaning is equal to "out of service" or "out of order", but it is only used when something is out of service in a bad way, like "broken" and not just "disabled". For a simple "on" or "off" operational state of the boiler and cooler i would prefer "An" and "Aus", because it leaves no room for possible misinterpretations.

[knuffifix]

I have added the change using "ein" and "aus" for the status translation. While checking, I also noticed that the temperature values ​​had no decimal places, so I adjusted the display accordingly.