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/messages/en.json

@@ -241,7 +241,7 @@
   "validation": {
     "required": "This field is required",
     "email": "Invalid email address",
-    "minLength": "Minimum {count} characters required",
+    "minLength": "Must be at least 8 characters",
     "maxLength": "Maximum {count} characters allowed",
     "pattern": "Invalid format",
     "passwordMismatch": "Passwords do not match"

frontend/messages/it.json

@@ -241,7 +241,7 @@
   "validation": {
     "required": "Questo campo è obbligatorio",
     "email": "Indirizzo email non valido",
-    "minLength": "Minimo {count} caratteri richiesti",
+    "minLength": "Deve contenere almeno 8 caratteri",
     "maxLength": "Massimo {count} caratteri consentiti",
     "pattern": "Formato non valido",
     "passwordMismatch": "Le password non corrispondono"