fix: replace hardcoded BADGE_BASE_URL with NEXT_PUBLIC_SITE_URL env var

- BADGE_BASE_URL was hardcoded to https://commitpulse.vercel.app/api/streak
- Badge URLs generated in customize page always pointed to production
- Replace with NEXT_PUBLIC_SITE_URL env var with production fallback
- Consistent with BASE_URL pattern in dashboard/[username]/page.tsx

Author: KaparthyReddy

app/customize/utils.ts

@@ -1,6 +1,6 @@
 import type { ExportFormat } from './types';
 
-const BADGE_BASE_URL = 'https://commitpulse.vercel.app/api/streak';
+const BADGE_BASE_URL = `${process.env.NEXT_PUBLIC_SITE_URL ?? 'https://commitpulse.vercel.app'}/api/streak`;
 
 /**
  * Removes the leading # from a hex color string.