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/capture-jfr.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Reproduces the main flagship recording: start a profile-settings recording,
+# drive real load, take a mid-flight snapshot to a DIFFERENT file (never the
+# recording's own destination -- see docs/output/09-dump-duplication-bug.txt
+# for what goes wrong if you do), then stop with its own filename.
+#
+# Usage: scripts/capture-jfr.sh <pid>
+set -euo pipefail
+cd "$(dirname "$0")/.."
+PID="${1:?usage: capture-jfr.sh <pid>}"
+mkdir -p recordings
+
+jcmd "$PID" JFR.start name=live settings=profile maxsize=256m
+
+scripts/load.sh cpu
+scripts/load.sh alloc
+scripts/load.sh lock
+
+jcmd "$PID" JFR.dump name=live filename="$(pwd)/recordings/mid-flight-snapshot.jfr"
+
+scripts/load.sh orders
+
+jcmd "$PID" JFR.stop name=live filename="$(pwd)/recordings/live-demo.jfr"
+
+echo "wrote recordings/live-demo.jfr and recordings/mid-flight-snapshot.jfr"