refactor: complete border unification across all components

- Add border styles to JsonEditor (CodeMirror) with theme-responsive colors
- Update all dialog header/footer dividers to use border-border-default
- Replace remaining border-border instances in settings components
- Ensure all borders (including separators and container borders) use unified design system
- All borders now consistently use CSS variables and respond to light/dark themes

src/components/settings/WindowSettings.tsx

@@ -52,7 +52,7 @@ function ToggleRow({
   onCheckedChange,
 }: ToggleRowProps) {
   return (
-    <div className="flex items-start justify-between gap-4 rounded-lg border border-border p-4">
+    <div className="flex items-start justify-between gap-4 rounded-lg border border-border-default p-4">
       <div className="space-y-1">
         <p className="text-sm font-medium leading-none">{title}</p>
         {description ? (