fix: replace all remaining old brand tokens (text-brand-dark, border-brand-border, bg-white opacity)

30 references to removed CSS variables: border-brand-border → border-[#1e2130],
text-brand-text-muted → text-[#4f5666], text-brand-dark → text-white,
bg-white/[0.04] → bg-[#191c25], hover:border-white/[0.12] → hover:border-[#2a2f3d].

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/scripts/ScriptParameterForm.tsx

@@ -43,7 +43,7 @@ export function ScriptParameterForm({ canGenerate }: Props) {
 
   if (parameters.length === 0) {
     return (
-      <div className="flex items-center gap-2 rounded-lg border border-border bg-white/[0.02] px-3 py-3">
+      <div className="flex items-center gap-2 rounded-lg border border-border bg-[#14161d] px-3 py-3">
         <Terminal size={14} className="text-muted-foreground shrink-0" />
         <p className="text-xs text-muted-foreground">
           This template has no parameters — click <span className="text-foreground font-medium">Generate</span> to produce the script.