Fix HF Space DDInter build defaults

[SPerekrestova]

Summary

• Add public pinned DDInter release defaults to the Dockerfile DB downloader stage so Hugging Face Spaces can build the generated mirror without GitHub Actions build args.
• Preserve CI/GCP override behavior through the same build args.
• Add a Dockerfile contract test for the Space-safe defaults.

Test Plan

• rtk uv run pytest tests/test_tier1_benchmark_workflow.py tests/test_download_interaction_db.py -q
• rtk uv run pytest tests/ --ignore=tests/test_rxnorm_client.py -q
• rtk git diff --check

Note: local Docker build could not run because the local Docker/OrbStack daemon socket is unavailable.