fix: Improve API initialization with lazy Supabase client and validation

- Move Supabase/Stripe initialization inside GET/POST handlers for lazy loading
- Add validation for missing environment variables in runtime
- Improve error handling in payment intent creation
- Clean up next.config.js environment variable configuration

This fixes potential build-time failures when environment variables are not available
during static generation.

next.config.js

@@ -14,7 +14,7 @@ const nextConfig = {
       {
         protocol: 'https',
         hostname: '**.supabase.co',
-      },
+  }
     ],
   },
   env: {
@@ -23,4 +23,7 @@ const nextConfig = {
   },
   compiler: {
     removeConsole: false, // Temporarily enable logs for debugging 500 errors
-module.exports = nextConfig
+  }
+}
+
+module.exports = nextConfig