fix: design system v4 polish — home icon, mobile hamburger, contrast, font-label cleanup

- Home sidebar icon: always cyan, bg-accent-dim only when route is "/"
- Mobile TopBar: add left padding so hamburger isn't hidden behind logo
- Landing page: bump card border color (#1e2130 → #2a2f3d) for better contrast
- Replace all font-label references (40 occurrences, 19 files) with font-mono or font-sans
- Remove deprecated --font-label CSS variable from index.css
- Convert hardcoded hex in layout inline styles to CSS variables (light-mode ready)
- Add @types/react-syntax-highlighter for script builder types

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

frontend/src/components/scripts/ScriptParameterForm.tsx

@@ -57,7 +57,7 @@ export function ScriptParameterForm({ canGenerate }: Props) {
       {ungrouped.map(renderParam)}
       {groupOrder.map(group => (
         <div key={group}>
-          <p className="font-label text-[0.625rem] uppercase tracking-[0.1em] text-muted-foreground mb-3">
+          <p className="font-sans text-[0.625rem] uppercase tracking-[0.1em] text-muted-foreground mb-3">
             {group}
           </p>
           <div className="flex flex-col gap-4">