* docs(billing): add design document for replacing SetupIntent cache
* docs(billing): add implementation plan for replacing SetupIntent cache
* feat(db): add gateway lookup stored procedures for Organization, Provider, and User
* feat(db): add gateway lookup indexes to Organization, Provider, and User table definitions
* chore(db): add SQL Server migration for gateway lookup indexes and stored procedures
* feat(repos): add gateway lookup methods to IOrganizationRepository and Dapper implementation
* feat(repos): add gateway lookup methods to IProviderRepository and Dapper implementation
* feat(repos): add gateway lookup methods to IUserRepository and Dapper implementation
* feat(repos): add EF OrganizationRepository gateway lookup methods and index configuration
* feat(repos): add EF ProviderRepository gateway lookup methods and index configuration
* feat(repos): add EF UserRepository gateway lookup methods and index configuration
* chore(db): add EF migrations for gateway lookup indexes
* refactor(billing): update SetupIntentSucceededHandler to use repository instead of cache
* refactor(billing): simplify StripeEventService by expanding customer on SetupIntent
* refactor(billing): query Stripe for SetupIntents by customer ID in GetPaymentMethodQuery
* refactor(billing): query Stripe for SetupIntents by customer ID in HasPaymentMethodQuery
* refactor(billing): update OrganizationBillingService to set customer on SetupIntent
* refactor(billing): update ProviderBillingService to set customer on SetupIntent and query by customer
* refactor(billing): update UpdatePaymentMethodCommand to set customer on SetupIntent
* refactor(billing): remove bank account support from CreatePremiumCloudHostedSubscriptionCommand
* refactor(billing): remove OrganizationBillingService.UpdatePaymentMethod dead code
* refactor(billing): remove ProviderBillingService.UpdatePaymentMethod
* refactor(billing): remove PremiumUserBillingService.UpdatePaymentMethod and UserService.ReplacePaymentMethodAsync
* refactor(billing): remove SubscriberService.UpdatePaymentSource and related dead code
* refactor(billing): update SubscriberService.GetPaymentSourceAsync to query Stripe by customer ID
Add Task 15a to plan - this was a missed requirement for updating
GetPaymentSourceAsync which still used the cache.
* refactor(billing): complete removal of PremiumUserBillingService.Finalize and UserService.SignUpPremiumAsync
* refactor(billing): remove ISetupIntentCache and SetupIntentDistributedCache
* chore: remove temporary planning documents
* chore: run dotnet format
* fix(billing): add MaxLength(50) to Provider gateway ID properties
* chore(db): add EF migrations for Provider gateway column lengths
* chore: run dotnet format
* chore: rename SQL migration for chronological order