Refactor i18n integration and update tests for improved localization

- Updated test components (`PasswordResetConfirmForm`, `PasswordChangeForm`) to use i18n keys directly, ensuring accurate validation messages.
- Refined translations in `it.json` to standardize format and content.
- Replaced text-based labels with localized strings in `PasswordResetRequestForm` and `RegisterForm`.
- Introduced `generateLocalizedMetadata` utility and updated layout metadata generation for locale-aware SEO.
- Enhanced e2e tests with locale-prefixed routes and updated assertions for consistency.
- Added comprehensive i18n documentation (`I18N.md`) for usage, architecture, and testing.

frontend/types/test-mocks.d.ts

@@ -0,0 +1,20 @@
+/**
+ * Type declarations for test mocks
+ * Augments modules to include mock exports for testing
+ */
+
+// Augment next-intl/navigation to include mock exports without removing original exports
+declare module 'next-intl/navigation' {
+  // Re-export all original exports
+  export * from 'next-intl/dist/types/navigation.react-client';
+
+  // Explicitly export createNavigation (it's a named export of a default, so export * might miss it)
+  export { createNavigation } from 'next-intl/dist/types/navigation/react-client/index';
+
+  // Add mock exports for testing
+  export const mockUsePathname: jest.Mock;
+  export const mockPush: jest.Mock;
+  export const mockReplace: jest.Mock;
+  export const mockUseRouter: jest.Mock;
+  export const mockRedirect: jest.Mock;
+}