Fix event capacity: no negative availability, sold-out enforcement, admin override

- Backend: use calculateAvailableSeats so availableSeats is never negative
- Backend: reject public booking when confirmed >= capacity; admin create/manual bypass capacity
- Frontend: spotsLeft = max(0, capacity - bookedCount), isSoldOut when bookedCount >= capacity
- Frontend: sold-out redirect on booking page, cap quantity by spotsLeft, never show negative

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

backend/src/routes/events.ts

@@ -4,7 +4,7 @@ import { z } from 'zod';
 import { db, dbGet, dbAll, events, tickets, payments, eventPaymentOverrides, emailLogs, invoices, siteSettings } from '../db/index.js';
 import { eq, desc, and, gte, sql } from 'drizzle-orm';
 import { requireAuth, getAuthUser } from '../lib/auth.js';
-import { generateId, getNow, convertBooleansForDb, toDbDate } from '../lib/utils.js';
+import { generateId, getNow, convertBooleansForDb, toDbDate, calculateAvailableSeats } from '../lib/utils.js';
 
 interface UserContext {
   id: string;
@@ -151,10 +151,11 @@ eventsRouter.get('/', async (c) => {
       );
       
       const normalized = normalizeEvent(event);
+      const bookedCount = ticketCount?.count || 0;
       return {
         ...normalized,
-        bookedCount: ticketCount?.count || 0,
-        availableSeats: normalized.capacity - (ticketCount?.count || 0),
+        bookedCount,
+        availableSeats: calculateAvailableSeats(normalized.capacity, bookedCount),
       };
     })
   );
@@ -189,11 +190,12 @@ eventsRouter.get('/:id', async (c) => {
   );
   
   const normalized = normalizeEvent(event);
+  const bookedCount = ticketCount?.count || 0;
   return c.json({
     event: {
       ...normalized,
-      bookedCount: ticketCount?.count || 0,
-      availableSeats: normalized.capacity - (ticketCount?.count || 0),
+      bookedCount,
+      availableSeats: calculateAvailableSeats(normalized.capacity, bookedCount),
     },
   });
 });
@@ -277,7 +279,7 @@ eventsRouter.get('/next/upcoming', async (c) => {
       event: {
         ...normalized,
         bookedCount,
-        availableSeats: normalized.capacity - bookedCount,
+        availableSeats: calculateAvailableSeats(normalized.capacity, bookedCount),
         isFeatured: true,
       },
     });
@@ -308,7 +310,7 @@ eventsRouter.get('/next/upcoming', async (c) => {
     event: {
       ...normalized,
       bookedCount,
-      availableSeats: normalized.capacity - bookedCount,
+      availableSeats: calculateAvailableSeats(normalized.capacity, bookedCount),
       isFeatured: false,
     },
   });