fix(loyalty): rename enrollment-success CTA from "continue shopping" to "back to home"

The loyalty storefront is a registration / wallet endpoint, not a
catalog — there's nothing to continue shopping toward. The button
already navigates to {{ base_url }} (the homepage), so the
destination was correct; only the wording was wrong.

Rename the i18n key continue_shopping -> back_to_home in
loyalty/enroll-success.html and all four locale files (en/fr/de/lb):

  EN: "Continue Shopping"        -> "Back to Home"
  FR: "Continuer mes achats"     -> "Retour à l'accueil"
  DE: "Weiter einkaufen"         -> "Zurück zur Startseite"
  LB: "Weider akafen"            -> "Zréck op d'Haaptsäit"

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/loyalty/locales/de.json

@@ -134,7 +134,7 @@
             "step_balance": "Prüfen Sie Ihren Kontostand online oder in der App",
             "step_redeem": "Lösen Sie Punkte gegen Prämien an allen unseren Standorten ein",
             "view_dashboard": "Mein Treue-Dashboard anzeigen",
-            "continue_shopping": "Weiter einkaufen"
+            "back_to_home": "Zurück zur Startseite"
         },
         "already_enrolled_title": "Sie sind bereits Mitglied!",
         "cross_location_message": "Ihre Karte gilt an allen unseren Standorten:",