Add comprehensive tests for authentication, settings, and password reset pages

- Introduced smoke tests for Login, Register, Password Reset, Password Reset Confirm, and Settings pages.
- Enhanced test coverage for all dynamic imports using mocks and added Jest exclusions for non-testable Next.js files.
- Added component-specific test files for better structure and maintainability.
- Improved test isolation by mocking navigation, providers, and rendering contexts.

frontend/src/app/providers.tsx

@@ -7,6 +7,7 @@ import { AuthInitializer } from '@/components/auth';
 
 // Lazy load devtools - only in local development (not in Docker), never in production
 // Set NEXT_PUBLIC_ENABLE_DEVTOOLS=true in .env.local to enable
+/* istanbul ignore next - Dev-only devtools, not tested in production */
 const ReactQueryDevtools =
   process.env.NODE_ENV === 'development' &&
   process.env.NEXT_PUBLIC_ENABLE_DEVTOOLS === 'true'