Port of the RTL slice of Rosmi720/XC_VM@f34b4808. When the active language is
right-to-left (ar/fa/ur/he), the admin and reseller shells and the login page
render mirrored:
- Translator::isRtl() reports whether a language (or the current one) is RTL.
- admin/reseller headers and login set <html dir="rtl"> and load the Cairo web
font + assets/xcvm/rtl.css only for RTL languages (a no-op for LTR).
- rtl.css mirrors navigation, cards, tables and forms.
- Arabic language file (ar.ini) so an RTL language is actually selectable.
Adapted to this tree: only the language-driven RTL was taken (not the fork's
navbar language switcher or the per-user RTL toggle); isRtl is unit-tested.
