Add flags: production JVM flag cheat sheet for Spring Boot on JDK 25/27

MaxRAMPercentage vs a hardcoded -Xmx, -XX:-UseContainerSupport, the
ActiveProcessorCount lie, and which diagnostic flags are worth leaving
on in prod, verified in real Docker containers on JDK 25 and JDK 27.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

flags/src/main/java/com/ankurm/flagsdemo/FlagsDemoApplication.java

@@ -0,0 +1,19 @@
+package com.ankurm.flagsdemo;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * Companion app for "JVM Flags for Spring Boot in Containers (JDK 25/27)" on ankurm.com.
+ * See docs/output/*.txt for the captured runs this post quotes from, and
+ * {@link JvmDiagnosticsController} for the live /internal/jvm-flags endpoint
+ * used to inspect what the JVM actually resolved its memory/GC flags to
+ * inside a running container. Delete that endpoint before shipping this to
+ * a real service — it exists for this demo only.
+ */
+@SpringBootApplication
+public class FlagsDemoApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(FlagsDemoApplication.class, args);
+    }
+}