Fix UK private-data credential deployment

[anth-volk]

Fixes #3865

Summary

• introduce the explicit PE_UK_PRIVATE_HF_READ_TOKEN GitHub credential and pe-uk-private-hf-read-token Secret Manager resource
• verify the Hugging Face identity, read-only permissions, and access to both required private UK repositories during release testing
• synchronize GitHub-owned runtime credentials into Secret Manager before Cloud Run deployments, without creating duplicate secret versions
• preserve the independently managed staging database credential while synchronizing the production database password
• verify stored secret values and Cloud Run runtime identity access without logging secret material
• add a manual staging or production synchronization workflow and document the complete credential path

Testing

• pytest tests/unit/test_cloud_run_deploy_scripts.py -q — 111 passed
• ruff format --check tests/unit/test_cloud_run_deploy_scripts.py tests/env_variables/test_environment_variables.py
• ruff check tests/unit/test_cloud_run_deploy_scripts.py tests/env_variables/test_environment_variables.py
• actionlint .github/workflows/push.yml .github/workflows/sync-cloud-run-secrets.yml
• bash -n .github/scripts/sync_cloud_run_secrets.sh
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.65%. Comparing base (0ebfc08) to head (b826ac6).

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3866       +/-   ##
===========================================
+ Coverage   45.76%   87.65%   +41.89%     
===========================================
  Files         182      197       +15     
  Lines       10812    11952     +1140     
  Branches     1837     2092      +255     
===========================================
+ Hits         4948    10477     +5529     
+ Misses       5456      901     -4555     
- Partials      408      574      +166     

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