Add resilience4j-circuit-breaker: Resilience4j 2.4.0 vs Spring Framework 7 core, on Boot 4.1

Companion module for the rewritten post 'Resilience4j Circuit Breaker in Spring Boot 4.1:
What It's Still For', reworked around Framework 7 now shipping @Retryable/@ConcurrencyLimit
in core. Covers what's still Resilience4j's job (circuit breaker, rate limiter, bulkhead's
bounded wait, fallback methods, Actuator/Micrometer metrics), the off-by-one between
maxAttempts and maxRetries, and two Boot-4.1 build breaks: spring-boot-starter-aop no longer
exists (renamed to spring-boot-starter-aspectj, proven with Maven Central metadata and the
renamed starter's own POM -- see resilience/docs/08-starter-aop-renamed-to-starter-aspectj.md
in this same repo), and the resulting fix uses that renamed starter directly rather than
assembling spring-aop + aspectjweaver by hand. Kept as its own module rather than a new
top-level repository, alongside the existing resilience/ module for the sibling Framework-7
post.

resilience4j-circuit-breaker/docs/output/05-actuator-health-tripped.txt

@@ -0,0 +1,7 @@
+Real /actuator/health and /actuator/circuitbreakers, captured over HTTP with the breaker actually OPEN
+======================================================================================================
+-- GET /actuator/health --
+{"components":{"circuitBreakers":{"status":"UNKNOWN"},"diskSpace":{"details":{"total":270553174016,"free":31630450688,"threshold":10485760,"path":"/home/claude/work/repos/spring-boot-demo-clone/resilience4j-circuit-breaker/.","exists":true},"status":"UP"},"livenessState":{"status":"UP"},"ping":{"status":"UP"},"readinessState":{"status":"UP"},"ssl":{"details":{"expiringChains":[],"invalidChains":[],"validChains":[]},"status":"UP"}},"groups":["liveness","readiness"],"status":"UP"}
+
+-- GET /actuator/circuitbreakers --
+{"circuitBreakers":{"paymentService":{"bufferedCalls":5,"failedCalls":5,"failureRate":"100.0%","failureRateThreshold":"50.0%","notPermittedCalls":1,"slowCallRate":"0.0%","slowCallRateThreshold":"100.0%","slowCalls":0,"slowFailedCalls":0,"state":"OPEN"}}}