Select personal or organization context
        ↓
Resolve BillingAccount
        ↓
Resolve/create Stripe Customer
        ↓
Create checkout for mapped price
        ↓
Customer completes Stripe payment flow
        ↓
Stripe updates subscription state
        ↓
Webhook processing
        ↓
Starfire subscription reconciliation
        ↓
Plan entitlements + credits provisioned