fix: reduce main layout height offset from 180px to 120px across all tools

Also restore scroll handling to ExportPanel and PresetLibrary, and
remove maxHeight cap from CodeSnippet in ExportPanel.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/animate/PresetLibrary.tsx

@@ -55,7 +55,7 @@ export function PresetLibrary({ onSelect }: Props) {
   const [category, setCategory] = useState<PresetCategory>(PRESET_CATEGORIES[0]);
 
   return (
-    <div className="space-y-3">
+    <div className="space-y-3 overflow-y-auto scrollbar-thin scrollbar-thumb-primary/20 scrollbar-track-transparent pr-0.5">
       <div className="flex items-center justify-between">
         <span className="text-[10px] font-semibold text-muted-foreground uppercase tracking-widest">Presets</span>
         <div className="flex glass rounded-lg p-0.5 gap-0.5">