Trust nginx proxy and drop hotlink response headers from Nest.

Rate limits use X-Forwarded-For behind prod nginx; hotlink security headers are set on /i/ in nginx only.

backend/src/main.ts

@@ -57,6 +57,8 @@ async function bootstrap() {
         credentials: true
     });
 
+    app.set('trust proxy', 1);
+
     await app.listen(port);
 }