fix(billing): ensure all tenants have valid Stripe customer IDs

backend/migrations/0002_tenant_stripe_customer_id_guards.sql

@@ -0,0 +1,19 @@
+CREATE UNIQUE INDEX IF NOT EXISTS tenant_stripe_customer_id_unique
+ON tenant(stripe_customer_id)
+WHERE stripe_customer_id <> '';
+
+CREATE TRIGGER IF NOT EXISTS tenant_stripe_customer_id_not_empty_insert
+BEFORE INSERT ON tenant
+FOR EACH ROW
+WHEN trim(NEW.stripe_customer_id) = ''
+BEGIN
+  SELECT RAISE(ABORT, 'stripe_customer_id cannot be empty');
+END;
+
+CREATE TRIGGER IF NOT EXISTS tenant_stripe_customer_id_not_empty_update
+BEFORE UPDATE OF stripe_customer_id ON tenant
+FOR EACH ROW
+WHEN trim(NEW.stripe_customer_id) = ''
+BEGIN
+  SELECT RAISE(ABORT, 'stripe_customer_id cannot be empty');
+END;