Define OPC UA demo namespace and data contract

[smithaldon1]

Summary

Closes #189.

• Adds an intentionally small OPC UA-style demo namespace for the simulator-backed manufacturer demo.
• Defines demo context nodes, tag names, node IDs, engineering units, normal/spec ranges, drift behavior, and normal/drifting examples.
• Maps the demo OPC UA-style tags to existing FactoryEvent process and quality event contracts without adding production namespace browsing or connector framework scope.
• Links the namespace document from the manufacturer demo runbook and records the change in the learning log.

Test Evidence

• .venv/bin/python -m pytest services/simulator/tests/test_opc_ua_demo_namespace_docs.py - 5 passed
• make test - 200 passed
• make lint - All checks passed
• make typecheck - compileall completed successfully
• make docs - Markdown-only docs target completed
• git diff --check - passed
• git diff --cached --check - passed

Docs Impact

• Added docs/demo/OPC_UA_DEMO_NAMESPACE.md.
• Updated docs/demo/MANUFACTURER_DEMO_RUNBOOK.md to link the new namespace/data-contract reference.
• Updated docs/LEARNING_LOG.md with what changed, why, data flow, and test guidance.

Follow-up Work

• Implement the future read-only OPC UA demo simulator or adapter against this namespace.
• Keep any future connector work limited to simulator/demo scope unless a separate issue expands it.

[smithaldon1]

Reviewed and approved for merge