Propagate chat session IDs to telemetry spans

[jbeard4]

Summary

• wrap dialog service OpenAI calls in explicit telemetry spans and attach the current chat session ID
• propagate session identifiers through OpenInference session context so downstream OpenAI spans are correlated
• pass session IDs from the chat router into the dialog service to include input and output payload metadata on spans

Testing

• pytest backend/tests (fails: ModuleNotFoundError: No module named 'db')

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Codex Task