Fix 3 Code Review findings on FRE-4574

- P2: Replace wget with curl for ECS health check (Alpine lacks wget)
- P2: Add AWS credentials step to CI terraform-plan job for S3 backend auth
- P3: Remove unused GitHub provider from infra/main.tf

Co-Authored-By: Paperclip <noreply@paperclip.ing>

scripts/load-test/services/api.js

@@ -3,7 +3,6 @@ import { check, group } from 'k6';
 import { Rate, Trend } from 'k6/metrics';
 import { getBaseUrl, getTargetRps, getDuration, defaultThresholds, checkResponse, randomString } from '../lib/common.js';
 
-const errorRate = new Rate('errors');
 const notificationLatency = new Trend('notification_p99');
 const correlationLatency = new Trend('correlation_p99');