fix: long unbroken transaction description broke Dashboard layout

Card had no min-width: 0, so as a direct CSS Grid child on the
Dashboard it would grow to fit nowrap (truncate) text instead of
letting the ellipsis kick in — classic grid blowout. Reproduced with
Playwright (scrollWidth 2143px vs 1440px viewport before the fix,
matches after). Fixing it on the shared Card primitive protects every
grid/flex layout that uses it, not just Dashboard.

frontend/src/components/ui/Card.tsx

@@ -4,7 +4,7 @@ import { cn } from "@/lib/utils";
 export function Card({ className, ...props }: HTMLAttributes<HTMLDivElement>) {
   return (
     <div
-      className={cn("rounded-xl border border-border bg-surface-1 shadow-sm", className)}
+      className={cn("min-w-0 rounded-xl border border-border bg-surface-1 shadow-sm", className)}
       {...props}
     />
   );