feat: internationalization support (i18n — IT/EN)

[nikazzio]

Summary

Add internationalization support to the Studio UI, starting with Italian (current default) and English.

Motivation

The UI is entirely in Italian. Adding English opens the project to an international audience of digital humanists, librarians, and researchers. The i18n infrastructure also enables future languages.

Proposed approach

• Create a translation dict/JSON file per language: translations/it.json, translations/en.json.
• Add a t(key) helper function available in all FastHTML/Jinja templates.
• Store language preference in browser localStorage + optional config setting.
• Language switcher in the header/settings.
• Start with IT (current strings) and EN.

Acceptance criteria

• All user-facing strings extracted to translation files
• Language switcher in UI header
• Italian and English fully translated
• Language preference persisted across sessions
• New strings default to Italian if translation is missing
• Developer docs on how to add a new language

Technical notes

• FastHTML approach: pass t function to template context, use t("key") in templates.
• Alternative: use Python gettext if preferring standard tooling.
• Keep translation keys as dotted paths: library.search.placeholder, studio.ocr.button, etc.
• Consider a scripts/extract_strings.py helper to find untranslated hardcoded strings.