Implement internationalization support across components

- Integrated `next-intl` for toast messages and locale handling in various components, including `Providers`, `CanvasUserMenu`, and `CreditOverview`.
- Replaced hardcoded strings with translation keys to enhance localization capabilities.
- Updated `RootLayout` to dynamically set the language attribute based on the user's locale.
- Ensured consistent user feedback through localized toast messages in actions such as sign-out, canvas operations, and billing notifications.

routing.ts

@@ -0,0 +1,7 @@
+import { defineRouting } from 'next-intl/routing';
+
+export const routing = defineRouting({
+  locales: ['de', 'en'],
+  defaultLocale: 'de',
+  localePrefix: 'never',
+});