Add observability: real OTLP metrics/traces to grafana/otel-lgtm, Docker Compose auto-wiring, and a dual-version (Boot 4.0 vs 4.1) proof of the new OTEL_* env var support

Companion module for the rewritten ankurm.com Prometheus/Grafana monitoring post. Verified
against a real running grafana/otel-lgtm container (not mocked): 8 real requests produce a real
orders_placed_total metric queried back from the bundled Prometheus-compatible API with zero
management.otlp.* properties, auto-wired entirely by Boot's Docker Compose service-connection
detection. Two real findings surfaced along the way and documented rather than smoothed over:
@Observed silently produces no span without an explicit ObservedAspect bean (AspectJ weaving
alone is not sufficient, despite Micrometer Tracing being active), and OTEL_EXPORTER_OTLP_ENDPOINT
already worked on Boot 4.0 via Micrometer's own OtlpConfig fallback -- what's actually new in 4.1
is the rest of the standard OTEL_* surface (verified with OTEL_METRIC_EXPORT_INTERVAL against
identical source compiled on both Boot 4.0.8 and 4.1.1).

Also fixes the root README's module table, which was missing a row for
resilience4j-circuit-breaker (added in a previous commit but never indexed here).

observability/docs/output/03-observed-needs-explicit-bean.txt

@@ -0,0 +1,32 @@
+OrderController#placeOrder is annotated @Observed(name = "place-order", contextualName =
+"order-controller#placeOrder"). Before ObservationConfig (an explicit ObservedAspect @Bean)
+existed in this repo, spring-boot-starter-opentelemetry, spring-boot-starter-aspectj (AspectJ
+weaver on the classpath) and micrometer-tracing were ALL already present and active -- and the
+annotation still did nothing. Real trace, fetched straight from Tempo's query API, before the fix:
+
+  $ curl -s "http://localhost:3200/api/traces/<trace-id>"
+  span: http post /orders/{id} | kind: SPAN_KIND_SERVER | parent: (root)
+  # one span. @Observed's child span never appears.
+
+After adding:
+
+  @Configuration(proxyBeanMethods = false)
+  class ObservationConfig {
+      @Bean
+      ObservedAspect observedAspect(ObservationRegistry registry) {
+          return new ObservedAspect(registry);
+      }
+  }
+
+Same annotation, same request, new trace:
+
+  $ curl -s "http://localhost:3200/api/traces/<trace-id>"
+  span: order-controller#placeOrder | kind: SPAN_KIND_INTERNAL | parent: <server-span-id>
+  span: http post /orders/{id}      | kind: SPAN_KIND_SERVER   | parent: (root)
+  # two spans. The @Observed child span now nests correctly under the HTTP server span.
+
+Spring Boot's autoconfiguration wires an ObservationRegistry bean for you the moment Micrometer
+Tracing is on the classpath -- it does NOT also register an ObservedAspect. AspectJ weaving
+being present is necessary but not sufficient; without the aspect bean there is nothing for the
+weaver to apply. This is easy to miss because the app starts cleanly, the HTTP server span still
+shows up, and nothing logs a warning -- the method-level span is just silently absent.