feat(ai-service): define and export PII_MODEL_VERSION in scrubber and…

[yunus-dev-codecrafter]

closes #268

Summary

Adds a pinned PII_MODEL_VERSION constant (1.0.0) to the PII scrubber and exposes it as a Prometheus pii_model_version{version="..."} gauge. This ensures reproducibility — two machines scrubbing the same text will report the same model version, and consumers (metrics endpoints, regression harness) can track which version is in use.

Testing

Ran the PII scrubber and regression test suite. The new test_pii_model_version_exported test reads the Prometheus registry directly (same pattern as test_circuit_breaker.py) to verify the metric is exported with the correct version label.

cd app/ai-service
pytest tests/test_pii_scrubber.py tests/test_pii_regression.py -v

The pytest_terminal_summary hook in conftest.py prints the version banner in every test run's footer.

Screenshots

N/A

Checklist

• Tests added or updated for new/changed behavior
• Existing tests pass
• No secrets, keys, or seed phrases committed
• Follows the coding conventions in the relevant service README
• PR is focused on a single concern

[kilodesodiq-arch]

Awesome work on this! Thanks for the contribution 🚀 Merging now.