feat(db): add Prisma schema with all models

Configure Prisma ORM with PostgreSQL database schema including:
- Organization, Site, Court models for multi-tenancy
- User with role-based access and Client for customers
- Booking and Payment models for reservations
- MembershipPlan and Membership for subscriptions
- Product, Sale, SaleItem, CashRegister for POS
- Tournament, TournamentInscription, Match for competitions
- All necessary enums, relations, indexes, and cascading deletes
- Prisma client singleton for Next.js

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/lib/db.ts

@@ -0,0 +1,18 @@
+import { PrismaClient } from '@prisma/client';
+
+declare global {
+  // eslint-disable-next-line no-var
+  var prisma: PrismaClient | undefined;
+}
+
+export const db =
+  globalThis.prisma ||
+  new PrismaClient({
+    log: process.env.NODE_ENV === 'development' ? ['query', 'error', 'warn'] : ['error'],
+  });
+
+if (process.env.NODE_ENV !== 'production') {
+  globalThis.prisma = db;
+}
+
+export default db;