Add OPC-UA read-only adapter foundation

[smithaldon1]

Closes #211

Summary

• Add an ingestion-layer OPC-UA read-only adapter foundation that loads enabled OPC-UA ProtocolConnectionProfile records from the local profile store.
• Read only the configured profile.opcua.node_ids through an injectable node reader; no browse, write, or arbitrary tag discovery path is added.
• Normalize configured numeric node values into process.measurement.recorded FactoryEvents with source metadata for connection profile ID, node ID, adapter name, and poll index.
• Add clear adapter errors for invalid profile stores, unavailable endpoints, bad configured nodes, and nonnumeric node values.
• Cover the foundation with fake-reader unit tests and a practical integration test against the local simulator-backed OPC-UA server.

Test Evidence

• .venv/bin/python -m pytest services/ingestion/tests/test_opcua_read_only_adapter.py - passed, 7 tests.
• make test-integration - passed, 74 tests.
• make lint - passed, Ruff found no issues after import formatting.
• make typecheck - passed, compileall completed across packages and services.
• make test - passed, 246 tests.
• make docs - passed; docs are Markdown-only and no checker is configured yet.
• git diff --check and git diff --cached --check - passed.

Docs Impact

• Updated services/ingestion/README.md with the OPC-UA read-only adapter foundation, source metadata behavior, safety boundary, and focused test command.
• Updated docs/LEARNING_LOG.md with what changed, why it matters, how the data flows, how to test it, and the next learning step.

Follow-up Work

• Implement explicit tag/source mapping lookup so mapping_reference supplies site, line, asset, unit, and signal metadata instead of adapter defaults.
• Add scheduling/runtime orchestration for adapter polling only after the connector runtime boundary is defined.
• Keep browse-all-tags, writeback, source discovery, and UI ingestion controls out of this adapter until their dedicated issues and ADR updates define those boundaries.

[smithaldon1]

Reviewed and approved for merge