Fix login button and improve CORS

- Fixed login URL from /auth/steam to /api/auth/steam
- Updated all Steam login buttons to custom green design with 'Login to Steam' text
- Enhanced CORS configuration with explicit preflight handling
- Added Steam image proxy endpoint for CORS-free image loading
- Improved environment variable management with .env.local support
- Added ENV_SETUP.md guide for environment configuration

config/index.js

@@ -1,6 +1,13 @@
 import dotenv from "dotenv";
+import { fileURLToPath } from "url";
+import { dirname, join } from "path";
 
-dotenv.config();
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+// Load .env.local first (for local development overrides), then .env
+dotenv.config({ path: join(__dirname, "..", ".env.local") });
+dotenv.config({ path: join(__dirname, "..", ".env") });
 
 export const config = {
   // Server