Add German (Deutsch) language support

### What problem are you experiencing?

The Locale settings currently offer English, French, Spanish, Arabic,
Turkish, Portuguese (BR), and Persian, but no German. As a German-speaking
user, I have to use the interface in English even though I'd prefer to
use it in my native language.

German is one of the most widely spoken languages in Europe, so adding
it would make ComfyUI more accessible to users in Germany, Austria, and
Switzerland.

### When does this problem occur?

- Every time I open the Settings menu and look for a German locale option
- When navigating menus, tooltips, and settings that are only available in English
- When trying to recommend ComfyUI to German-speaking friends/colleagues
who are less comfortable with English technical terms

### How often do you encounter this problem?

Multiple times per day

### How much does this problem affect your workflow?

Blocks me from completing tasks

### Current workarounds

_No response_

### Ideas for solutions (Optional)

_No response_

### Additional context

_No response_

Start at the Settings menu's locale list and inspect how the existing English, French, Spanish, Arabic, Turkish, Portuguese (BR), and Persian options are represented. Add German (Deutsch) and verify that menus, tooltips, and settings are available in German, then check the interface for untranslated areas.

Written by the indexing model from the issue text.