ReviewEligibility

Pure engagement-gating logic for the in-app review prompt.

A prompt is eligible only when ALL hold:

• the account is at least ReviewGateConfig.minAccountAgeDays old (since first open),

• the user has performed at least ReviewGateConfig.minInteractions meaningful interactions,

• and at least ReviewGateConfig.cooldownDays have passed since the last prompt (if ever shown).

No platform deps, the counters live in a ReviewState supplied by the caller (persisted however the app likes — DataStore, NSUserDefaults, …), so this is trivially unit-testable.