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>

load-tests/darkwatch-auth/.gitignore

@@ -0,0 +1,5 @@
+# k6 load test results
+results/
+
+# Local environment overrides
+.env