RecordGroupSection: sentence-case group header

Drops the tracking-wide uppercase micro-label treatment for a 13px
sentence-case header — softer fit for consumer surfaces.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/index.tsx

@@ -249,7 +249,7 @@ export function RecordGroupSection({
   return (
     <section data-slot="record-group" className={cn("space-y-2", className)}>
       <div className="flex items-baseline gap-2 px-1">
-        <h3 className="text-xs font-semibold tracking-wide text-muted-foreground uppercase">
+        <h3 className="text-[0.8125rem] font-semibold text-muted-foreground">
           {label}
         </h3>
         {locked ? (