Integrate durable trace commitments with Logger

[areshand]

Summary

• keep the existing trace exporter and add a Logger-owned post-upload commitment hook with a metadata-only S3 outbox in the same existing trace location
• submit deterministic trace.artifact_exported events without trace bodies and expose independent Logger backlog status
• publish the standalone Logger image and extend scoped/idempotency/checkpoint verification coverage

Validation

• cargo test --locked -p multiagent-logger
• python3 tests/test_trace_commitment.py
• npm test --prefix control-server
• python3 -m py_compile logger/trace_commitment.py tests/test_trace_commitment.py
• git diff --check

Deployment

No new S3 bucket is introduced. The commitment manifest, outbox event, and delivered marker are separate objects under the existing per-session trace prefix. InternalServices only owns the Logger workload, credentials, storage, network policy, and invocation of the logger/trace_commitment.py helper after the existing exporter succeeds. No deployment or merge is performed by this PR.