i18n: add Catalan (ca) translation

[cuquet]

Summary

This PR adds full Catalan (ca) language support to Sync-in.

Changes

New translation file

• frontend/src/i18n/ca.json — Complete Catalan translation covering all UI strings:
  • Authentication (login, password, 2FA, recovery codes)
  • File management (upload, download, copy, move, delete, trash)
  • Spaces and shares
  • Groups and users administration
  • Guests and links
  • Synchronization and scheduling
  • Markdown editor
  • Editor integration (OnlyOffice, Collabora)
  • Preferences and settings
  • Notifications and events

Language registration

• backend/src/common/i18n.ts — Added ca to LANG_SUPPORTED
• frontend/src/i18n/l10n.ts — Added ca: 'Català' to i18nLanguageText
• frontend/src/i18n/lib/bs.i18n.ts — Registered caLocale for ngx-bootstrap datepicker
• frontend/src/i18n/lib/dayjs.i18n.ts — Registered ca locale for dayjs date formatting

Testing

• ✅ ca.json validated as proper JSON
• ✅ Follows the exact structure of existing translation files (e.g., es.json, nl.json)
• ✅ Language code ca follows ISO 639-1 standard
• ✅ Alphabetical ordering preserved in all language lists

Notes

The translation has been carefully reviewed to use proper Catalan terminology consistent with the rest of the Sync-in interface. Technical terms (WebDAV, OnlyOffice, etc.) are kept in their original form where appropriate.

I'm happy to make any adjustments requested by the maintainers.

Related

Closes #[issue number if any]

[cla-assistant]

All committers have signed the CLA.

[johaven]

Hi @cuquet, thank you for this pull request. We’re going to approve it.

Would it also be possible for you to add this language to the desktop client in the following repository: https://github.com/Sync-in/desktop? It follows the same localization format.

Thanks again for your contribution!

[johaven]

@cuquet it looks like a translation file is missing from the following directory: backend/src/applications/notifications/i18n

[cuquet]

@cuquet it looks like a translation file is missing from the following directory: backend/src/applications/notifications/i18n

Done! I've added the missing translation file at:
backend/src/applications/notifications/i18n/ca.ts

Thanks for pointing it out.

[johaven]

Thanks! If you'd like, feel free to open a PR on the desktop app repository to add the translations.