Add jfr-demo: JFR + Mission Control profiling of a live Spring Boot app

Custom OrderProcessed event, CPU/allocation/lock workloads, a diagnostic
endpoint over the JVM's live FlightRecorder state, a JUnit test using the
jdk.jfr.Recording API, and nine captured recordings (flagship, mid-flight
snapshot, isolated vs concurrent threshold comparisons, and a real
dump+stop duplication bug) with their docs/output/*.txt transcripts.

scripts/run.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Build and start the demo app in the foreground (or detached with -d).
+# Usage: scripts/run.sh [-d]
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+for p in $(ps -eo pid,cmd | grep '[j]fr-demo.jar' | awk '{print $1}'); do
+  echo "killing previous instance: $p"
+  kill -9 "$p"
+done
+
+mvn -q -B -DskipTests package
+
+if [[ "${1:-}" == "-d" ]]; then
+  setsid nohup java -jar target/jfr-demo.jar > /tmp/jfr-demo.log 2>&1 < /dev/null &
+  echo "started detached, pid $!"
+  for i in $(seq 1 30); do
+    code=$(curl -s -o /dev/null -w '%{http_code}' localhost:8080/api/jfr/recordings || true)
+    [[ "$code" == "200" ]] && { echo "up after ${i}s"; exit 0; }
+    sleep 1
+  done
+  echo "app did not come up in time, see /tmp/jfr-demo.log" >&2
+  exit 1
+else
+  exec java -jar target/jfr-demo.jar
+fi