refactor: replace raw SQL with Drizzle in all tests

- Replace TestPayKit.pool with TestPayKit.database (Drizzle instance)
- Convert all pool.query() calls to Drizzle query builder in e2e tests
- Add drizzle-orm dependency to e2e package
- Fix waitForWebhook timestamp comparison with gt() operator
- Fix getSubscriptionByProviderSubscriptionId ordering (createdAt DESC)