fix(activities): relabel "Get invoice" → "Proceed" on PurchaseTicket

The lightning rail's CTA in PurchaseTicketDialog now reads
"Proceed" (or "Proceed (N tickets)" for multi-quantity) instead
of "Get invoice". Matches the language used on the fiat rails
("Continue to Stripe checkout" etc.) and reads as a generic
forward action regardless of which payment path the user picks.

src/modules/activities/components/PurchaseTicketDialog.vue

@@ -443,7 +443,7 @@ onUnmounted(() => {
           </template>
           <template v-else>
             <Zap class="w-4 h-4 mr-2" />
-            {{ quantity > 1 ? `Get invoice for ${quantity} tickets` : 'Get invoice' }}
+            {{ quantity > 1 ? `Proceed buying (${quantity} tickets)` : 'Proceed' }}
           </template>
         </Button>
       </div>