fix: handle possibly undefined strkUsdRate in OrderBook

Author: Victor Amaya

src/app/(app)/trade/components/OrderBook.tsx

@@ -300,7 +300,7 @@ export function OrderBook({ pairId, pair, onOrderClick }: OrderBookProps) {
       <div className="grid grid-cols-3 gap-2 px-4 py-2 text-xs text-gray-500 border-b border-surface-border/50">
         <div className="flex items-center gap-1">
           Price ({pair.quote})
-          {orderBook.strkUsdRate > 0 && (
+          {(orderBook.strkUsdRate ?? 0) > 0 && (
             <span className="text-emerald-500/70 flex items-center">
               <DollarSign className="w-3 h-3" />
             </span>
@@ -367,9 +367,9 @@ export function OrderBook({ pairId, pair, onOrderClick }: OrderBookProps) {
                 <div className="text-right">
                   <span className="text-gray-500 text-xs">Spread</span>
                   <div className="text-white font-mono">{orderBook.spread}</div>
-                  {orderBook.strkUsdRate > 0 && (
+                  {(orderBook.strkUsdRate ?? 0) > 0 && (
                     <div className="text-xs text-gray-600">
-                      STRK = ${orderBook.strkUsdRate.toFixed(3)}
+                      STRK = ${orderBook.strkUsdRate!.toFixed(3)}
                     </div>
                   )}
                 </div>
@@ -406,7 +406,7 @@ export function OrderBook({ pairId, pair, onOrderClick }: OrderBookProps) {
 
             {/* Full depth indicator with USD info */}
             <div className="px-4 py-3 text-center text-xs text-gray-600 border-t border-surface-border/30">
-              {orderBook.strkUsdRate > 0 ? (
+              {(orderBook.strkUsdRate ?? 0) > 0 ? (
                 <span>On-chain orderbook • USD prices via Pragma Oracle</span>
               ) : (
                 <span>Full orderbook depth from on-chain</span>