Update PolicyEngine bundle to 4.18.5

[anth-volk]

Summary

• Update API v1 to policyengine[models]==4.18.5 and refresh uv.lock.
• Add a lightweight PR gate that checks the simulation API supports the updated .py bundle before other PR checks run.
• Use the same lightweight .py bundle support check in push-time staging and production guards.
• Make bundle version tests compare against the installed .py manifest instead of hard-coded current package versions.

Notes

The live simulation gateway currently advertises 4.18.3 but not 4.18.5, so this PR's new support gate is expected to fail until the updated simulation API deployment publishes the 4.18.5 route.

Verification

• uv run pytest tests/unit/test_constants.py tests/unit/test_cloud_run_deploy_scripts.py
• uv run ruff check tests/unit/test_constants.py tests/unit/test_cloud_run_deploy_scripts.py
• uv run ruff format tests/unit/test_constants.py tests/unit/test_cloud_run_deploy_scripts.py
• bash -n .github/check-policyengine-bundle-supported.sh
• bash -n .github/request-simulation-model-versions.sh
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.81%. Comparing base (ab8156d) to head (63bb169).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3713   +/-   ##
=======================================
  Coverage   78.81%   78.81%           
=======================================
  Files          71       71           
  Lines        4320     4320           
  Branches      804      804           
=======================================
  Hits         3405     3405           
  Misses        702      702           
  Partials      213      213           

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