refactor(theming): replace red-* palette with semantic error-* tokens

Sweep 30 files: text/bg/border/ring/from/to/via/fill/stroke/shadow/divide/decoration/
outline/placeholder-red-N → -error-N. All red usages were semantically error/danger
(no brand red), so tokens now flow through the design-system CSS variables and respond
to palette overrides.

src/api/menuLayout.ts

@@ -43,7 +43,7 @@ export const STYLE_OPTIONS = [
   { value: 'default' as const, colorClass: 'bg-dark-500' },
   { value: 'primary' as const, colorClass: 'bg-blue-500' },
   { value: 'success' as const, colorClass: 'bg-success-500' },
-  { value: 'danger' as const, colorClass: 'bg-red-500' },
+  { value: 'danger' as const, colorClass: 'bg-error-500' },
 ];
 
 const DEFAULT_CONFIG: MenuConfig = { rows: [] };