Spring Boot 4 Actuator in production: endpoints, security, custom health indicators

Companion repository for the ankurm.com article. Every transcript in docs/output/
was produced by running this project; scripts/run-all.sh regenerates all of them.

Verified against Spring Boot 4.1.1 / Framework 7.0.9 / Security 7.1.1 /
Micrometer 1.17.1 / kafka-clients 4.2.1 on Temurin JDK 25.0.4.1+1.

docs/output/09-kafka-timeout.txt.tuned

@@ -0,0 +1,15 @@
+### Kafka health check against an unreachable broker -- tuned
+
+$ time curl -s http://localhost:8080/actuator/health/kafka
+{
+    "details": {
+        "bootstrap": "localhost:9092",
+        "tuned": true,
+        "error": "TimeoutException: null",
+        "probeMs": 1500,
+        "budgetMs": 1500
+    },
+    "status": "DOWN"
+}
+
+wall clock: 1.6 s