test: temp_postgres_store fixture never clears user_entitlements

[FlyM1ss]

Status: deferred 2026-09-02 in PR #436 (defer rule D1)

What: temp_postgres_store (dashboard/backend/tests/test_users_postgres.py:92-97) deletes password_reset_requests, email_change_requests, auth_sessions, and users between tests, but never user_entitlements. Under a full-file run against a real Postgres (TEST_POSTGRES_URL), leftover rows fail test_entitlements_missing_user_is_user_not_found_postgres and test_credit_spend_for_missing_user_postgres via cross-test pollution. Invisible on CI/local runs without a live PG (@pg_only skips).

Why deferred: D1 — pre-existing fixture gap in the entitlements/credits tests, untouched by PR #436's password-reset diff (found while live-verifying the PR's tests against postgres:16, which pass).

Next-session entry point: dashboard/backend/tests/test_users_postgres.py:92-97 — add DELETE FROM user_entitlements (and any credit-ledger tables) to the fixture wipe, re-run the full file against a live PG. ~15 min.

[FlyM1ss]

Fix in #439, with the mechanism corrected: the leftover-rows story doesn't reproduce on any repo-created schema — user_entitlements has carried REFERENCES users(id) ON DELETE CASCADE since its first commit (e5daadda), so the fixture's DELETE FROM users already cascade-clears it (34/34 live postgres:18 runs green, fresh + reused DB, with and without the fix). The explicit wipe lands anyway as hardening for long-lived local dev DBs mutated by a review branch's divergent DDL, completing the fixture's existing explicit-wipe pattern.