Configure for self-hosted deployment

- Add environment variable support for Supabase and Pakasir configurations
- Create Docker configuration with Nginx for production deployment
- Add .env.example with all required environment variables
- Remove hardcoded URLs from Supabase client and Checkout component
- Add Docker and Nginx configuration files for Coolify deployment

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/pages/Checkout.tsx

@@ -14,7 +14,7 @@ import { Trash2, CreditCard, Loader2, QrCode, Wallet } from "lucide-react";
 import { QRCodeSVG } from "qrcode.react";
 
 // Pakasir configuration
-const PAKASIR_PROJECT_SLUG = "dewengoding";
+const PAKASIR_PROJECT_SLUG = import.meta.env.VITE_PAKASIR_PROJECT_SLUG || "dewengoding";
 const SANDBOX_API_KEY = "iP13osgh7lAzWWIPsj7TbW5M3iGEAQMo";
 
 // Centralized API key retrieval - uses env var with sandbox fallback