Fix Python 3.10 syntax incompatibilities breaking the build job

[Copilot]

The build job was failing in the flake8 syntax gate under GitHub Actions' Python 3.10 environment. The failure came from invalid multiline f-string patterns and a placeholder orchestrator.py implementation that could not be parsed.

• Python 3.10 syntax cleanup

  • Rewrote multiline f-strings into parser-safe string construction in the files flagged by CI:
    • agents.py
    • langgraph/embeddings.py
    • langgraph/ingestion.py
    • models.py
    • src/attestation_agent.py
    • src/fleet_manager.py

• Demo orchestrator repair

  • Replaced the invalid placeholder implementation in orchestrator.py with a minimal, lint-safe demo orchestrator.
  • Kept the file scoped to the existing demo path: security check, telemetry wrapper, and reusable IntakeAgent wiring.

• Stress script payload formatting

  • Replaced hand-built interpolated JSON in tests/stress/mqtt_flood.py with json.dumps(...) to avoid syntax fragility and preserve the emitted payload structure.

Example of the syntax adjustment pattern:

print(
    f"Generating sovereign embeddings for {len(texts_to_embed)} "
    f"chunks. Tenant: {tenant_id}..."
)