Completa i18n IT/EN/FR/DE/ES su sito pubblico, area autenticata e admin.

Tutte le view marketing, legali, viewer, dashboard e admin usano t(); mailer utente-facing e flash localizzati; admin con LocaleResolver e selettore lingua.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/views/billing/invoice_mailer/invoice_pdf.text.erb

@@ -1,9 +1,12 @@
-Buongiorno,
+<%= t("mailers.invoice.hello") %>
 
-in allegato la fattura <%= @invoice.display_number %> del <%= l(@invoice.issued_on, locale: :it, format: :long) %>
-(<%= @invoice.formatted_amount %>) per <%= @club.billing_legal_name.presence || @club.name %>.
+<%= t("mailers.invoice.body_text",
+      number: @invoice.display_number,
+      date: l(@invoice.issued_on, format: :long),
+      amount: @invoice.formatted_amount,
+      club: @club.billing_legal_name.presence || @club.name) %>
 
-È disponibile anche in Abbonamento sul sito Match Live TV.
+<%= t("mailers.invoice.also_text") %>
 
-Grazie,
-Match Live TV
+<%= t("mailers.invoice.thanks") %>
+<%= t("mailers.invoice.signoff") %>