bug(quota): free monthly resets skip limit warm-up

[HulianBuligon]

What happened?

Free plans expose their long quota as a monthly window, but the background reset-confirmed warm-up path only received secondary usage rows. When usage refresh recorded an exhausted-to-reset monthly transition, the opted-in warm-up was therefore skipped.

Expected behavior

When long-window limit warm-up is enabled for a free-plan account, a confirmed monthly quota reset should send at most one warm-up request and persist the attempt with window="monthly".

Reproduction

1. Enable limit warm-up globally and for a free-plan account.
2. Select long-window warm-up.
3. Record an exhausted monthly usage sample.
4. Run background usage refresh so it records an available monthly sample with a later reset_at.
5. Observe that no monthly warm-up attempt is created.

Safety constraint

If there is no previous monthly sample (for example, immediately after a paid-to-free plan transition), a stale secondary sample must not be compared with the first monthly sample as if one quota window reset.

Tracking

Fix proposed in #1504.

[Soju06]

Verified against current main: the gap is still there. run_after_usage_refresh only ever receives before_secondary/after_secondary (app/core/usage/refresh_scheduler.py:189-240), and the warm-up service normalizes long-window selection to ("primary", "secondary") only (app/modules/limit_warmup/service.py:646-647), so a free plan's monthly reset never produces a candidate — while the monthly-aware _select_long_window_entry policy already exists on main but only in reconcile_recoverable_account_statuses (refresh_scheduler.py:313-324). #1504 at current HEAD covers both this defect and the safety constraint above: commit 929c0d4 (cross-window guard) refuses to compare a stale secondary snapshot against the first monthly sample. This should close via #1504.