Fix 4 Code Review findings on FRE-4928: dead heredoc, token warmup, summary path, .gitignore

- P2: Remove dead heredoc from run.sh mixed scenario
- P2: Add setup() warmup to seed real tokens for standalone scenarios
- P3: Replace handleSummary file output with --summary-export in run.sh
- P3: Add .gitignore for k6 results and .env
- Fix stray closing brace in scripts/load-test/lib/common.js

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

scripts/load-test/lib/common.js

@@ -45,6 +45,4 @@ export const autoscaleMetric = new Trend('autoscale_vu_count');
 
 export function recordAutoscaleMetric(vuCount) {
   autoscaleMetric.add(vuCount);
-}
-  return result;
 }