fix(public-site): honor dark theme surface colors

frontend/src/pages/admin/CMSPage.tsx

@@ -303,7 +303,7 @@ export const CMSPage: React.FC = () => {
     const branding = publicSiteBranding || publicSiteDefaults?.branding;
     const substitutedHtml = applyBrandTokens(publicSiteSanitizedHtml, branding);
     const inlineStyles = [
-      branding ? `:root {\n  --brand-primary: ${branding.colors.primary};\n  --brand-accent: ${branding.colors.accent};\n  --brand-background: ${branding.colors.background};\n  --brand-text: ${branding.colors.text};\n}` : '',
+      branding ? `:root {\n  --brand-primary: ${branding.colors.primary};\n  --brand-accent: ${branding.colors.accent};\n  --brand-background: ${branding.colors.background};\n  --brand-text: ${branding.colors.text};\n  --brand-surface: ${branding.colors.surface || '#ffffff'};\n  --brand-elevated: ${branding.colors.elevated || '#f5f5f5'};\n  --brand-border: ${branding.colors.border || '#e5e5e5'};\n  --brand-muted-text: ${branding.colors.mutedText || '#737373'};\n}` : '',
       publicSiteBaseCss,
       publicSiteSanitizedCss ? `/* Custom styles */\n${publicSiteSanitizedCss}` : ''
     ].filter(Boolean).join('\n\n');

frontend/src/services/settings.service.ts

@@ -152,6 +152,10 @@ export interface PublicSiteBranding {
     accent: string;
     background: string;
     text: string;
+    surface?: string;
+    elevated?: string;
+    border?: string;
+    mutedText?: string;
   };
 }