fix(i18n): localize the mobile profile-sheet menu labels
The mobile profile menu had hardcoded Dutch labels (Account, Beheer, Nieuwe post, Thema,
Donker/Licht, Uitloggen) so they didn't translate on EN/DE sites. They now use t().
- src/views/partials/profile-sheet.ejs — Account/Admin/New post/Logout reuse the existing
nav.* keys; the theme item + its JS state label use new nav.theme_label/nav.dark/nav.light
- src/services/i18n.js — add nav.theme_label, nav.dark, nav.light (nl/en/de)
Co-Authored-By: Claude <noreply@…>