Add jdk27-perf: the same Spring Boot service measured on JDK 25 and JDK 27

Live heap, throughput, p99 and startup across four configurations, including opt-in and opt-out of
compact object headers.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WzVQ6zFh9cuLPj9RSbRH8U

jdk27-perf/scripts/live-set.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# Usage: live-set.sh <java-home> <label> [jvm args...]
+# Starts the server, forces a full GC through /live, and prints the heap still in use.
+# This is the resident data set: 3,000,000 two-int records plus the Spring Boot baseline.
+set -u
+JH=$1; LABEL=$2; shift 2
+JAR="$(dirname "$0")/../target/jdk27-perf-1.0.0.jar"
+PORT=${PORT:-18082}
+"$JH/bin/java" "$@" -jar "$JAR" --server.port=$PORT --spring.main.banner-mode=off \
+    --logging.level.root=WARN > /dev/null 2>&1 &
+PID=$!
+until [ "$(curl -s -o /dev/null -m 2 -w '%{http_code}' "localhost:$PORT/stats")" = 200 ]; do sleep 0.05; done
+live=$(curl -s "localhost:$PORT/live" | sed -n 's/.*"liveHeapMiB":\([0-9]*\).*/\1/p')
+echo "$LABEL: live heap after full GC ${live} MiB"
+kill $PID 2>/dev/null; wait $PID 2>/dev/null