Add the service migration 20261012_badge_subscriptions: the subscription
charges table, the ledger's charge_id, and the payment's subscription state,
check time and Play token, replacing three subscription columns nothing
wrote. The ledger now stores and reads back charge credits, and the badge
credential response gains an optional subscription state that older clients
ignore and that reads an unknown state without failing. Nothing writes a
charge or a state yet, so no behaviour changes.
Run: 001-badge-subscriptions, slice 2