Use admin-set sale end dates in countdown banner

- Countdown now uses actual sale_end_date from database instead of hardcoded Sunday
- Shows time until earliest sale end date when multiple sales are active
- Falls back to next Sunday if no end dates are set
- Banner now reflects real deadlines set in admin panel

src/components/SaleCountdown.tsx

@@ -12,9 +12,10 @@ interface TimeLeft {
 interface SaleCountdownProps {
   hasActiveSale: boolean;
   maxSalePercentage?: number;
+  saleEndDate?: string | null;
 }
 
-export function SaleCountdown({ hasActiveSale, maxSalePercentage = 5 }: SaleCountdownProps) {
+export function SaleCountdown({ hasActiveSale, maxSalePercentage = 5, saleEndDate }: SaleCountdownProps) {
   const [timeLeft, setTimeLeft] = useState<TimeLeft>({ days: 0, hours: 0, minutes: 0, seconds: 0 });
   const [mounted, setMounted] = useState(false);
 
@@ -26,16 +27,24 @@ export function SaleCountdown({ hasActiveSale, maxSalePercentage = 5 }: SaleCoun
     if (!mounted) return;
 
     const calculateTimeLeft = (): TimeLeft => {
-      // Get next Sunday at 23:59:59
       const now = new Date();
-      const nextSunday = new Date();
-      const daysUntilSunday = (7 - now.getDay()) % 7;
-      const targetDay = daysUntilSunday === 0 ? 7 : daysUntilSunday; // If today is Sunday, target next Sunday
-      
-      nextSunday.setDate(now.getDate() + targetDay);
-      nextSunday.setHours(23, 59, 59, 999);
+      let targetDate: Date;
 
-      const difference = nextSunday.getTime() - now.getTime();
+      if (saleEndDate) {
+        // Use the sale end date from admin
+        targetDate = new Date(saleEndDate);
+      } else {
+        // Fallback to next Sunday at 23:59:59
+        const nextSunday = new Date();
+        const daysUntilSunday = (7 - now.getDay()) % 7;
+        const targetDay = daysUntilSunday === 0 ? 7 : daysUntilSunday;
+        
+        nextSunday.setDate(now.getDate() + targetDay);
+        nextSunday.setHours(23, 59, 59, 999);
+        targetDate = nextSunday;
+      }
+
+      const difference = targetDate.getTime() - now.getTime();
 
       if (difference > 0) {
         return {