fix(config): ensure is_demo_mode is persisted in site.config.json and typed in SiteConfig interface

src/pages/admin/index.astro

@@ -72,12 +72,13 @@ const presets = Object.values(THEME_PRESETS);
                 <textarea id="metaDescription" rows="2" class="w-full glass-panel bg-slate-950/60 rounded-xl p-3 text-xs text-white focus:outline-none focus:border-sky-400 resize-none">{siteConfig.metaDescription}</textarea>
               </div>
               <label class="flex items-center gap-3 pt-2 p-3 bg-amber-500/10 border border-amber-500/20 rounded-xl cursor-pointer">
-                <input type="checkbox" id="isDemoMode" checked={(siteConfig as any).is_demo_mode ?? false} class="rounded text-amber-400 focus:ring-0 h-4 w-4" />
+                <input type="checkbox" id="isDemoMode" checked={!!siteConfig.is_demo_mode} class="rounded text-amber-400 focus:ring-0 h-4 w-4" />
                 <div>
                   <span class="text-xs text-amber-400 font-bold block">🎭 Demo-Modus aktivieren</span>
                   <span class="text-[10px] text-slate-400">Zeigt einen festen Demo-Hinweis für Interessenten auf der Live-Website</span>
                 </div>
               </label>
+
             </div>
 
             <h3 class="text-xs font-bold text-slate-400 uppercase tracking-wider pt-2 border-t border-white/10">Unternehmens-Stammdaten (Dynamic Data Binding)</h3>

src/utils/configLoader.ts

@@ -73,6 +73,7 @@ export interface SiteConfig {
   sectionsOrder: string[];
 
   sectionsDetails?: SectionConfig[];
+  is_demo_mode?: boolean;
   site_info?: {
     title?: string;
     company_name?: string;
@@ -117,6 +118,8 @@ export interface SmtpConfig {
 export const FALLBACK_SITE_CONFIG: SiteConfig = {
   siteName: 'N&D IT Solutions',
   metaDescription: 'High-Performance Webdesign & Digital Solutions - 100% DSGVO-konform.',
+  is_demo_mode: false,
+
   header: {
     brandName: 'N&D',
     brandHighlight: 'i-t SOLUTIONS',