fix(textarea): reserve scrollbar gutter on both edges for symmetric padding

The shared shadcn Textarea wrapper used `scrollbar-gutter-stable`, which
reserves space for the scrollbar only on the inline-end edge. Combined
with symmetric `px-3` padding, content appeared left-shifted inside
the textarea — visible in Vue Nodes 2.0 Note nodes as asymmetric right
vs left padding.

Switch to `scrollbar-gutter-both` (CSS `scrollbar-gutter: stable
both-edges`) so the reserved gutter is matched on both sides. Preserves
the no-reflow guarantee from #12280.

src/components/ui/textarea/Textarea.vue

@@ -23,7 +23,7 @@ defineExpose({
     v-model="modelValue"
     :class="
       cn(
-        'flex min-h-16 w-full scrollbar-gutter-stable rounded-lg border-none bg-secondary-background px-3 py-2 text-sm text-base-foreground placeholder:text-muted-foreground focus-visible:ring-1 focus-visible:ring-border-default focus-visible:outline-none disabled:pointer-events-none disabled:opacity-50',
+        'flex min-h-16 w-full scrollbar-gutter-both rounded-lg border-none bg-secondary-background px-3 py-2 text-sm text-base-foreground placeholder:text-muted-foreground focus-visible:ring-1 focus-visible:ring-border-default focus-visible:outline-none disabled:pointer-events-none disabled:opacity-50',
         className
       )
     "