feat: complete Spanish (es) translations and fix hardcoded English labels

[sandraR01]

What changes I've made

Frontend translations (frontend/src/locales/es.po / es.js)

• Translated all missing strings to Spanish
• Replaced "boleto" with "entrada" (correct term for event tickets in Spanish)
• Fixed gender agreement throughout (un→una, el→la, del→de la, oculto→oculta, etc.)
• Fixed terminology: Role→Rol, Monto→Cantidad, Terminado→Completado, Reintegrado→Reembolsado
• Added missing translation for "Invited" → "Invitado"

Hardcoded status labels

• AttendeeStatusBadge: Status values (ACTIVE, CANCELLED, AWAITING_PAYMENT) now use t macro for translation
• OrderStatusBadge: All order/payment/refund statuses now use translated labels instead of raw API values
• Users table: Role (ADMIN/ORGANIZER) and status (ACTIVE/INVITED/INACTIVE) now translated

Date localization

• Added DatesProvider with locale prop to App.tsx for calendar localization
• Made relativeDate() locale-aware using dayjs locale
• Created dynamic getDateTimePickerFormat() for locale-specific date/time picker formats
• Added dateLocales.ts with per-locale format configurations

Backend translations (backend/lang/es.json)

• Replaced "boleto" with "entrada" and fixed gender agreement

Why I've made these changes

To improve Spanish translations

How I've tested these changes

• All 2340 frontend strings translated (0 missing)
• npx lingui compile passes without errors
• TypeScript validation passes

Checklist

• I have read the contributing guidelines.
• My code follows the coding standards of the project.
• I have tested my changes, and they work as expected.
• I understand that this PR will be closed if I do not follow the contributor guidelines and if this PR template is left unedited.

I have read the CLA Document and I hereby sign the CLA

[daveearley]

Thank you very much for these changes!