📧 fix: Case-Insensitive Domain Matching (#9868)

* chore: move domain related functions to `packages/api`

* fix: isEmailDomainAllowed for case-insensitive domain matching

- Added tests to validate case-insensitive matching for email domains in various scenarios.
- Updated isEmailDomainAllowed function to convert email domains to lowercase for consistent comparison.
- Improved handling of null/undefined entries in allowedDomains.

* ci: Mock isEmailDomainAllowed in samlStrategy tests

- Added a mock implementation for isEmailDomainAllowed to return true in samlStrategy tests, ensuring consistent behavior during test execution.

* ci: Update import of isEmailDomainAllowed in ldapStrategy tests

- Changed the import of isEmailDomainAllowed from the domains service to the api package for consistency and to reflect recent refactoring.

api/strategies/samlStrategy.spec.js

@@ -26,6 +26,7 @@ jest.mock('~/server/services/Config', () => ({
   getAppConfig: jest.fn().mockResolvedValue({}),
 }));
 jest.mock('@librechat/api', () => ({
+  isEmailDomainAllowed: jest.fn(() => true),
   getBalanceConfig: jest.fn(() => ({
     tokenCredits: 1000,
     startBalance: 1000,