This commit introduces internationalization for several pages:
- AuthCallbackPage.vue
- ChoresPage.vue (a comprehensive page with many elements)
- ErrorNotFound.vue
- GroupDetailPage.vue (including sub-sections for members, invites, chores summary, and expenses summary)
Key changes:
- Integrated `useI18n` in each listed page to handle translatable strings.
- Replaced hardcoded text in templates and relevant script sections (notifications, dynamic messages, fallbacks, etc.) with `t('key')` calls.
- Added new translation keys, organized under page-specific namespaces (e.g., `authCallbackPage`, `choresPage`, `errorNotFoundPage`, `groupDetailPage`), to `fe/src/i18n/en.json`.
- Added corresponding keys with placeholder translations (prefixed with DE:, FR:, ES:) to `fe/src/i18n/de.json`, `fe/src/i18n/fr.json`, and `fe/src/i18n/es.json`.
- Reused existing translation keys (e.g., for chore frequency options) where applicable.
