Spring Boot startup time: bean-by-bean diagnosis, and one directory per post

Adds spring-boot-startup-time/, the companion project for BLOG-618: a runnable
Spring Boot 4.1.1 application on JDK 25 that installs BufferingApplicationStartup
and FlightRecorderApplicationStartup behind a system property, and a /diag/startup
endpoint that computes step self time -- the number /actuator/startup does not give
you and the one that names the actual culprits.

Captured under docs/output/: the step tree sorted both ways, the same startup as JFR
events, a +5000-class experiment putting 0.11 ms per scanned class on the classpath
scan tax, the silent truncation a 2048-step buffer performs, and JDK 25 AOT cache
timings (6.93 s to 4.82 s). Post body and metadata live in post/.

Moves the existing Actuator project into actuator-in-production/ so the repository
holds one directory per article; the root README is now an index.

actuator-in-production/scripts/run.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Start the application with the given comma-separated profiles and block until it answers.
+#   ./scripts/run.sh                 # defaults
+#   ./scripts/run.sh exposeall,open  # every endpoint, no authentication
+set -euo pipefail
+cd "$(dirname "$0")/.."
+source scripts/env.sh
+PROFILES="${1:-}"
+LOG="${LOG:-/tmp/actuator-demo.log}"
+
+scripts/stop.sh
+
+ARGS=(-B -o org.springframework.boot:spring-boot-maven-plugin:run)
+[ -n "$PROFILES" ] && ARGS+=("-Dspring-boot.run.profiles=$PROFILES")
+
+setsid nohup "$MVN" "${ARGS[@]}" > "$LOG" 2>&1 < /dev/null &
+
+READY_URL="${READY_URL:-http://127.0.0.1:${APP_PORT}/orders/count}"
+for _ in $(seq 1 90); do
+  code=$(curl -s -o /dev/null -w '%{http_code}' -u ops:ops-password "$READY_URL" || true)
+  [ "$code" != "000" ] && [ -n "$code" ] && exit 0
+  sleep 2
+done
+echo "application did not start; tail of $LOG:" >&2
+tail -40 "$LOG" >&2
+exit 1