Add k6 load test scripts for Darkwatch authentication endpoints (FRE-4928)

- darkwatch-auth.js: k6 script testing POST /auth/login, /auth/logout, /auth/refresh
- P99 thresholds: login <200ms, logout <100ms, refresh <150ms
- Config: 500 req/s sustained for 5 minutes
- Mixed workload scenario + individual endpoint scenarios
- .env.example and run.sh for execution
Co-Authored-By: Paperclip <noreply@paperclip.ing>

load-tests/darkwatch-auth/run.sh

@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+# Run k6 load tests for Darkwatch authentication endpoints
+# Usage: ./run.sh [scenario]
+#   scenario: mixed (default), login, logout, refresh
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR"
+
+# Load environment variables from .env if present
+if [[ -f .env ]]; then
+  set -a
+  source .env
+  set +a
+fi
+
+SCENARIO="${1:-mixed}"
+OUTPUT_DIR="${SCRIPT_DIR}/results"
+TIMESTAMP="$(date +%Y%m%d-%H%M%S)"
+
+mkdir -p "$OUTPUT_DIR"
+
+echo "=== Darkwatch Auth Load Test ==="
+echo "Scenario: $SCENARIO"
+echo "Target RPS: ${TARGET_RPS:-500}"
+echo "Duration: ${DURATION:-300s}"
+echo "Base URL: ${DARKWATCH_BASE_URL:-http://localhost:3000}"
+echo ""
+
+case "$SCENARIO" in
+  mixed)
+    k6 run darkwatch-auth.js \
+      --out json="$OUTPUT_DIR/results-${TIMESTAMP}.json" \
+      <<EOF
+EOF
+    ;;
+  login)
+    k6 run --scenario login_only darkwatch-auth.js \
+      --out json="$OUTPUT_DIR/results-${TIMESTAMP}.json"
+    ;;
+  logout)
+    k6 run --scenario logout_only darkwatch-auth.js \
+      --out json="$OUTPUT_DIR/results-${TIMESTAMP}.json"
+    ;;
+  refresh)
+    k6 run --scenario refresh_only darkwatch-auth.js \
+      --out json="$OUTPUT_DIR/results-${TIMESTAMP}.json"
+    ;;
+  *)
+    echo "Unknown scenario: $SCENARIO"
+    echo "Available: mixed, login, logout, refresh"
+    exit 1
+    ;;
+esac
+
+EXIT_CODE=$?
+
+if [[ $EXIT_CODE -eq 0 ]]; then
+  echo ""
+  echo "✅ All thresholds passed!"
+  echo "Results saved to: $OUTPUT_DIR/results-${TIMESTAMP}.json"
+else
+  echo ""
+  echo "❌ Thresholds failed. Check output above."
+  echo "Results saved to: $OUTPUT_DIR/results-${TIMESTAMP}.json"
+fi
+
+exit $EXIT_CODE