refactor(bookings): simplify capacity tracking to use seats

Replace 'pax' booking mode with 'seat'
Consolidate inventory summary to track only seat counts
Update database schema and UI for seat-centric capacity

app/pages/receipt/[token].vue

@@ -427,7 +427,7 @@ async function openBatchShare() {
           </div>
 
           <UButton
-            label="Share Seat"
+            label="Share Seats"
             icon="i-lucide-share-2"
             class="w-full justify-center sm:w-auto"
             :disabled="!availableSeats.length || shareSeatsLoading || Boolean(seatActionId)"