OTLP and External Observability

BatchIn now supports OTLP/HTTP JSON and protobuf trace ingest, and it can export spans from the unified trace control plane as OTLP for Grafana, Datadog, Jaeger, and existing observability stacks.

Now: native and OTLP spans land in the same trace control plane

Ingress and export: OTLP/HTTP JSON, protobuf, plus export by trace/run/prompt/source

Goal: plug into existing observability tools instead of rebuilding them