feat(i18n): fix remaining hardcoded strings and add login page switcher
- Add 9 missing translation keys to de/en/es.json:
doc_file_error_preview, doc_download_title, doc_tag_filter_title,
doc_conversation_title, doc_preview_iframe_title, doc_image_alt,
doc_no_date, person_merge_will_be_deleted, admin_user_delete_confirm
- documents/[id]/+page.svelte: replace 6 hardcoded strings with m.*()
- persons/[id]/+page.svelte: replace "wird gelöscht." and "Kein Datum"
- admin/+page.svelte: replace confirm() string with m.admin_user_delete_confirm()
- login/+page.svelte: add top-right DE/EN/ES language switcher (Option B)
and wire existing login_* keys to the form labels
Closes #12
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
20313de4e9