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

server/api/public/bookings.post.ts

@@ -12,7 +12,7 @@ export default defineEventHandler(async (event): Promise<CreateBookingResponse>
   const body = await readBody<{
     customerName?: string
     customerPhone?: string
-    bookingMode?: BookingMode
+    bookingMode?: BookingMode | string | null
     quantity?: number
     ticketType?: TicketType
     personInChargeId?: string

server/api/public/bookings/[token]/confirm.post.ts

@@ -18,7 +18,7 @@ export default defineEventHandler(async (event) => {
 
   const summary = await getBookingInventorySummary()
 
-  if (summary.leftCapacitySeats !== null && existingBooking.seatCount > summary.leftCapacitySeats) {
+  if (summary.leftSeats !== null && existingBooking.seatCount > summary.leftSeats) {
     httpError(409, 'Not enough capacity left to confirm this booking')
   }