Add OPC UA demo ingestion worker

[smithaldon1]

Summary

• Adds a demo-only OPC UA ingestion worker that polls the configured local demo OPC UA namespace and writes normalized FactoryEvents to the JSONL event store.
• Maps demo tag context into site, line, asset, work order, batch, and product-aware events for the existing ingestion and Process Sentinel path.
• Adds a make opcua-demo-ingest entry point plus focused docs and learning-log coverage.

Closes #192

Test Evidence

• .venv/bin/python -m pytest services/ingestion/tests/test_opcua_demo_worker.py -> 5 passed in 3.20s
• make lint -> All checks passed
• make typecheck -> compileall completed successfully
• make docs -> Markdown-only docs checker message; no configured docs checker yet
• make test -> 209 passed in 14.76s
• make opcua-demo-ingest OPCUA_ENDPOINT=opc.tcp://127.0.0.1:4841/ofi/demo OPCUA_POLL_COUNT=1 OPCUA_POLL_INTERVAL=0 OPCUA_EVENTS_STORE=/private/tmp/opcua_issue192_events.jsonl -> emitted 6 events to /private/tmp/opcua_issue192_events.jsonl
• docker compose -f infra/docker/docker-compose.yml up --build -d opcua-simulator could not run in this environment because the Docker daemon socket was unavailable: dial unix /Users/aldonsmith/.docker/run/docker.sock: connect: no such file or directory

Docs Impact

• Updated services/ingestion/README.md with the worker command, expected output path, polling interval, expected summary, and demo-only boundary.
• Linked the ingestion-worker docs from docs/demo/MANUFACTURER_DEMO_RUNBOOK.md.
• Added a learning entry to docs/LEARNING_LOG.md.

Follow-up Work

• Add an end-to-end demo smoke target that starts the Dockerized OPC UA simulator, polls events, and runs Process Sentinel over the generated store once Docker is available in CI/local validation.

[smithaldon1]

Reviewed and approved for merge