One-time script to convert existing annual Member records from the legacy
monthly-equivalent interpretation to cadence-unit. Multiplies
contributionAmount by 12 for billingCadence='annual' members.
Companion to commit 5023fb1 which dropped the server's ×12 on annual
recurringAmount. Must run after deploy, before annual members renew.
Idempotent via a transient `contributionAmountConverted: true` marker
field on each migrated doc — re-runs are safe. Dry-run by default;
`--apply` to write. Skips null/undefined contributionAmount, logs $0
amounts as no-ops.
