@opentelemetry/api adapter for the Tracer interface

[pathosDev]

The OTel-style tracing layer (#10) ships with the framework's own minimal `Tracer` interface plus a `RecordingTracer` reference impl. It does not depend on `@opentelemetry/api`.

Most production users will want to plug into the real OTel SDK (Jaeger / Tempo / Honeycomb / Datadog). Instead of asking each user to write the same adapter, ship one in the framework as a thin optional wrapper.

Scope:

• New file `src/tracing/OtelAdapter.ts` (peer-dep: `@opentelemetry/api`).
• Exports `otelTracer(otelApi: trace.Tracer)` that returns our `Tracer` shape.
• Methods translate:
  • `startSpan(name, opts)` → `otelApi.startSpan(name, opts)`
  • `withActiveSpan(span, fn)` → `context.with(trace.setSpan(context.active(), span), fn)`
  • `injectContext` / `extractContext` → `propagation.inject` / `propagation.extract` with the W3C `TraceContextPropagator`
• Tests against the OTel SDK's `InMemorySpanExporter` so we can assert spans without HTTP exporters.
• Example: `examples/management/otel-jaeger.ts` showing OTLP-HTTP exporter setup.

Estimate: 1-2 days.

Verification:

• Round-trip an actor.receive span through the adapter, observe in the OTel exporter that traceId / spanId / parent are preserved.
• Cross-wire propagation: A's tell with the OTel-tracer enabled produces a `traceparent` header B can extract, then chain into B's actor.receive span.