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.

docs/output/11-broken-event-pattern.txt

@@ -0,0 +1,15 @@
+$ java -cp target/classes com.ankurm.jfr.events.BrokenEventPatternDemo
+calls:               200
+exceptions thrown:    41
+events committed:     159
+expected if lossless: 200
+events missing:       41 (== exceptions thrown)
+
+BrokenEventPattern.processWithoutTryFinally() has no try/finally around
+event.commit(); when riskyStep() throws (about one call in five, by design),
+execution leaves the method from the catch in the demo driver, not from the line
+that would have called commit(). The event threshold was forced to 0 ms for this
+run specifically to rule out "the event was just too fast to pass the default
+threshold" as an alternative explanation -- every one of the 41 missing events is
+attributable to the missing try/finally, not to filtering. No exception, log line,
+or JFR.check output calls this out: the only way to notice is to count.