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/scripts/run.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+# Starts the app on :8080. Boot's Docker Compose support auto-starts compose.yaml's
+# grafana/otel-lgtm container the first time this runs (needs Docker) and wires the OTLP
+# metrics/traces/logs exporters to it -- no management.otlp.* properties needed.
+#   ./scripts/run.sh              # default 0.10 trace sampling
+#   ./scripts/run.sh fulltrace    # 1.0 trace sampling -- see docs/03-otel-env-vars.md
+set -euo pipefail
+cd "$(dirname "$0")/.."
+PROFILE="${1:-}"
+if [ -n "$PROFILE" ]; then
+  mvn -q -Dspring-boot.run.profiles="$PROFILE" spring-boot:run
+else
+  mvn -q spring-boot:run
+fi