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/reproduce-dump-bug.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# Reproduces the dump/stop duplication trap documented in
+# docs/output/09-dump-duplication-bug.txt. Do not copy this pattern.
+#
+# Usage: scripts/reproduce-dump-bug.sh <pid>
+set -euo pipefail
+cd "$(dirname "$0")/.."
+PID="${1:?usage: reproduce-dump-bug.sh <pid>}"
+mkdir -p recordings
+DEST="$(pwd)/recordings/dump-duplication-bug.jfr"
+
+jcmd "$PID" JFR.start name=live settings=profile filename="$DEST" maxsize=256m
+scripts/load.sh all
+# BUG: dumping to the SAME path the recording is already configured to write to...
+jcmd "$PID" JFR.dump name=live filename="$DEST"
+# ...then stopping with no filename, which falls back to that same path.
+jcmd "$PID" JFR.stop name=live
+
+echo "wrote $DEST -- every event in it is duplicated. See docs/output/09-dump-duplication-bug.txt"