51890e1aa5
Audit follow-up to the Spanish-locale commit: `CustomerDetailPage` had a hardcoded `<option>` list for the customer's preferred-language selector — 5 entries (en/de/nl/pt/ru) that were missing both fr (an existing gap) and es (the new one). Every other language selector in the frontend (the navbar `LanguageSelector`, the `GeneralTab` default- language dropdown, the `EmailConfigPage` per-language tabs) already reads from the shared `SUPPORTED_LANGUAGES` constant, so adding es there was enough for those. This one had drifted. Now mapped from `SUPPORTED_LANGUAGES` so future locales only need to touch one place.