Add sale countdown timer expiring next Sunday

- Created SaleCountdown component with real-time countdown
- Displays days, hours, minutes, seconds until sale ends
- Responsive design with fire emoji and urgency messaging
- Auto-calculates next Sunday at 23:59:59
- Positioned prominently above filament table

app/page.tsx

@@ -2,6 +2,7 @@
 
 import { useState, useEffect } from 'react';
 import { FilamentTableV2 } from '../src/components/FilamentTableV2';
+import { SaleCountdown } from '../src/components/SaleCountdown';
 import { Filament } from '../src/types/filament';
 import { filamentService } from '../src/services/api';
 import { trackEvent } from '../src/components/MatomoAnalytics';
@@ -174,6 +175,8 @@ export default function Home() {
           </a>
         </div>
         
+        <SaleCountdown />
+        
         <FilamentTableV2 
           key={resetKey}
           filaments={filaments}