[PM-31040] Replace ISetupIntentCache with customer-based approach (#6954)

* 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

util/Migrator/DbScripts/2026-02-18_00_AddGatewayLookupIndexesAndProcs.sql

@@ -0,0 +1,141 @@
+-- Add indexes for Organization
+IF NOT EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_Organization_GatewayCustomerId')
+BEGIN
+    CREATE NONCLUSTERED INDEX [IX_Organization_GatewayCustomerId]
+        ON [dbo].[Organization]([GatewayCustomerId])
+        WHERE [GatewayCustomerId] IS NOT NULL;
+END
+GO
+
+IF NOT EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_Organization_GatewaySubscriptionId')
+BEGIN
+    CREATE NONCLUSTERED INDEX [IX_Organization_GatewaySubscriptionId]
+        ON [dbo].[Organization]([GatewaySubscriptionId])
+        WHERE [GatewaySubscriptionId] IS NOT NULL;
+END
+GO
+
+-- Add indexes for Provider
+IF NOT EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_Provider_GatewayCustomerId')
+BEGIN
+    CREATE NONCLUSTERED INDEX [IX_Provider_GatewayCustomerId]
+        ON [dbo].[Provider]([GatewayCustomerId])
+        WHERE [GatewayCustomerId] IS NOT NULL;
+END
+GO
+
+IF NOT EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_Provider_GatewaySubscriptionId')
+BEGIN
+    CREATE NONCLUSTERED INDEX [IX_Provider_GatewaySubscriptionId]
+        ON [dbo].[Provider]([GatewaySubscriptionId])
+        WHERE [GatewaySubscriptionId] IS NOT NULL;
+END
+GO
+
+-- Add indexes for User
+IF NOT EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_User_GatewayCustomerId')
+BEGIN
+    CREATE NONCLUSTERED INDEX [IX_User_GatewayCustomerId]
+        ON [dbo].[User]([GatewayCustomerId])
+        WHERE [GatewayCustomerId] IS NOT NULL;
+END
+GO
+
+IF NOT EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_User_GatewaySubscriptionId')
+BEGIN
+    CREATE NONCLUSTERED INDEX [IX_User_GatewaySubscriptionId]
+        ON [dbo].[User]([GatewaySubscriptionId])
+        WHERE [GatewaySubscriptionId] IS NOT NULL;
+END
+GO
+
+-- Create stored procedures
+CREATE OR ALTER PROCEDURE [dbo].[Organization_ReadByGatewayCustomerId]
+    @GatewayCustomerId VARCHAR(50)
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    SELECT
+        *
+    FROM
+        [dbo].[OrganizationView]
+    WHERE
+        [GatewayCustomerId] = @GatewayCustomerId
+END
+GO
+
+CREATE OR ALTER PROCEDURE [dbo].[Organization_ReadByGatewaySubscriptionId]
+    @GatewaySubscriptionId VARCHAR(50)
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    SELECT
+        *
+    FROM
+        [dbo].[OrganizationView]
+    WHERE
+        [GatewaySubscriptionId] = @GatewaySubscriptionId
+END
+GO
+
+CREATE OR ALTER PROCEDURE [dbo].[Provider_ReadByGatewayCustomerId]
+    @GatewayCustomerId VARCHAR(50)
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    SELECT
+        *
+    FROM
+        [dbo].[ProviderView]
+    WHERE
+        [GatewayCustomerId] = @GatewayCustomerId
+END
+GO
+
+CREATE OR ALTER PROCEDURE [dbo].[Provider_ReadByGatewaySubscriptionId]
+    @GatewaySubscriptionId VARCHAR(50)
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    SELECT
+        *
+    FROM
+        [dbo].[ProviderView]
+    WHERE
+        [GatewaySubscriptionId] = @GatewaySubscriptionId
+END
+GO
+
+CREATE OR ALTER PROCEDURE [dbo].[User_ReadByGatewayCustomerId]
+    @GatewayCustomerId VARCHAR(50)
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    SELECT
+        *
+    FROM
+        [dbo].[UserView]
+    WHERE
+        [GatewayCustomerId] = @GatewayCustomerId
+END
+GO
+
+CREATE OR ALTER PROCEDURE [dbo].[User_ReadByGatewaySubscriptionId]
+    @GatewaySubscriptionId VARCHAR(50)
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    SELECT
+        *
+    FROM
+        [dbo].[UserView]
+    WHERE
+        [GatewaySubscriptionId] = @GatewaySubscriptionId
+END
+GO