Lighter content panel (Polar look), equal-height cards, hide card scrollbar

- globals.css: lighten --background (content panel) and deepen --sidebar so
  the panel reads as a lighter neutral charcoal floating on a near-black rail,
  matching the Polar reference. Pure lightness change; panel stays below
  --card so cards still pop.
- patient-cards.tsx: row uses items-stretch so all cards share one height
  (no more ragged/taller cards); add no-scrollbar to hide the horizontal
  scrollbar while keeping scroll.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/components/chat/patient-cards.tsx

@@ -266,7 +266,7 @@ export function PatientResult({ status, fileNumber, patient }: PatientResultProp
   }
 
   return (
-    <div className="flex w-full snap-x items-start gap-4 overflow-x-auto pb-2">
+    <div className="no-scrollbar flex w-full snap-x items-stretch gap-4 overflow-x-auto pb-2">
       {status === "loading" || !patient ? (
         <LoadingCards />
       ) : (