fix(tests): _rate_limiter singleton not reset in test teardown -- rate limit state leaks between tests #297

Summary

_configure_settings teardown in tests/conftest.py at line ~272 resets _api_key_store but not the _rate_limiter singleton. Tests that monkeypatch get_rate_limiter or the _rate_limiter module-level variable leave the modified instance in place for subsequent tests, causing state leaks.

Fix

tests/conftest.py teardown: also reset the _rate_limiter singleton:
import backend.app.security.rate_limit as _rl_mod
_rl_mod._rate_limiter = None
Or call monkeypatch.setattr(_rl_mod, "_rate_limiter", None) in the fixture.

Impact

Rate-limiter state from one test leaks into subsequent tests, causing intermittent failures when window counts from a previous test affect the rate-limit check in a later test.