Bootstrap Credits with Stripe

Add a complete prepaid credit system with Stripe payment integration to a Phoenix 1.8 app.

What Gets Created

1. Credit Balances — Per-account balance with optimistic locking
2. Credit Transactions — Immutable append-only ledger (deductions, additions, adjustments)
3. Usage Events — Per-operation tracking with cost, cache status, metadata
4. Billing — Credit pack configuration, Stripe PaymentIntent creation, customer lifecycle
5. Stripe Webhook — Signature verification, event routing, idempotent credit fulfillment
6. PgFlow Job — Async credit fulfillment with deduplication
7. LiveView Pages — Purchase page with Stripe Payment Element, balance/history page
8. JS Hook — Stripe.js lazy-loading and Payment Element mounting

Prerequisites