Update legal documents and localization for compliance and clarity

- Updated .env.example with legal operator details for compliance.
- Refactored Impressum, Privacy, and Terms pages to utilize a new LegalDocument component for improved structure and maintainability.
- Enhanced localization files to include legal content in both German and English, ensuring accurate representation of legal information.
- Improved i18n handling to support locale detection from Accept-Language headers.

apps/webui/src/lib/i18n.ts

@@ -1,18 +1,20 @@
-import { cookies } from 'next/headers';
+import { cookies, headers } from 'next/headers';
 import deMessages from '@/messages/de.json';
 import enMessages from '@/messages/en.json';
+import legalDe from '@/messages/legal-de.json';
+import legalEn from '@/messages/legal-en.json';
 import { env } from './env';
 
 export type Locale = 'de' | 'en';
 
 export const LOCALE_COOKIE_NAME = 'nexumi_locale';
 
-export type Messages = typeof enMessages;
+export const MESSAGES = {
+  de: { ...deMessages, legal: legalDe },
+  en: { ...enMessages, legal: legalEn }
+} as const;
 
-export const MESSAGES: Record<Locale, Messages> = {
-  de: deMessages,
-  en: enMessages
-};
+export type Messages = (typeof MESSAGES)['en'];
 
 function resolve(messages: Messages, key: string): string | undefined {
   const value = key.split('.').reduce<unknown>((acc, part) => {
@@ -43,12 +45,45 @@ function isLocale(value: string | undefined): value is Locale {
   return value === 'de' || value === 'en';
 }
 
+function localeFromAcceptLanguage(header: string | null): Locale | undefined {
+  if (!header) {
+    return undefined;
+  }
+
+  const preferred = header
+    .split(',')
+    .map((part) => {
+      const [tag, qValue] = part.trim().split(';q=');
+      return { lang: tag.trim().toLowerCase().slice(0, 2), q: qValue ? Number(qValue) : 1 };
+    })
+    .filter((entry) => entry.lang.length === 2 && !Number.isNaN(entry.q))
+    .sort((a, b) => b.q - a.q);
+
+  for (const entry of preferred) {
+    if (isLocale(entry.lang)) {
+      return entry.lang;
+    }
+  }
+
+  return undefined;
+}
+
 /**
  * Resolves the active locale for the current request from the
- * `nexumi_locale` cookie, falling back to the server's configured default.
+ * `nexumi_locale` cookie, then Accept-Language, then the server default.
  */
 export async function getLocale(): Promise<Locale> {
   const cookieStore = await cookies();
   const cookieLocale = cookieStore.get(LOCALE_COOKIE_NAME)?.value;
-  return isLocale(cookieLocale) ? cookieLocale : env.DEFAULT_LOCALE;
+  if (isLocale(cookieLocale)) {
+    return cookieLocale;
+  }
+
+  const headerList = await headers();
+  const fromHeader = localeFromAcceptLanguage(headerList.get('accept-language'));
+  if (fromHeader) {
+    return fromHeader;
+  }
+
+  return env.DEFAULT_LOCALE;
 }