List user policies within the page limit in the live staging test

[anth-volk]

Fixes #3943

Summary

• The live staging test's _policy_ids helper asked GET /v2/user-policies for limit=1000. The Public API caps limit at MAXIMUM_QUERY_LIMIT (500), so the request got 422 and test_live_unauthenticated_users_round_trip_and_upgrade failed.
• That test runs in "Deploy and test staging Cloud Run candidate", so the staging candidate was never promoted and the production steps were skipped. Run 38793955936 carries Stage 12A: Sign-in identity and v1-anchored user associations #3891 and Relay simulation run stage and progress on computing economy responses #3916, which are merged but not deployed.
• The helper now imports MAXIMUM_QUERY_LIMIT from policyengine_api.query_parameters and asks for that, so the test and the API's limit can't drift apart again.

Testing

• Not run locally: this is a live integration test that runs against the deployed staging candidate. The deploy run after this merges exercises it.
• ruff format and ruff check pass on the changed file.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.49%. Comparing base (fc31955) to head (74d9afb).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3944       +/-   ##
===========================================
+ Coverage   47.76%   85.49%   +37.73%     
===========================================
  Files         239      255       +16     
  Lines       13374    14667     +1293     
  Branches     2300     2580      +280     
===========================================
+ Hits         6388    12540     +6152     
+ Misses       6363     1320     -5043     
- Partials      623      807      +184     

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