Fix load test scenarios, runner, and CI threshold checks

- Add constant-arrival-rate scenarios to all 4 service scripts (api,
  darkwatch, spamshield, voiceprint) to enforce 500 req/s target
- Fix defaultThresholds() to return { thresholds: {...} } so
  http_req_duration and errors thresholds are actually applied
- Rewrite run-all.sh: per-service summary files, proper env var
  passing (DURATION, API_TOKEN), fixed threshold aggregation
- Update CI workflow threshold check jq to match new threshold-results
  structure (.services.<name>.exitCode)

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

scripts/load-test/lib/common.js

@@ -16,8 +16,10 @@ export function getDuration() {
 
 export function defaultThresholds(p99ms) {
   return {
-    http_req_duration: [`p(99)<${p99ms}`],
-    errors: ['rate<0.01'],
+    thresholds: {
+      http_req_duration: [`p(99)<${p99ms}`],
+      errors: ['rate<0.01'],
+    },
   };
 }