feat(db): add seed script with demo data

Add comprehensive seed script for testing the application with realistic demo data:
- Organization "Padel Pro Demo"
- 3 sites (Norte, Sur, Centro) with different schedules
- 2 courts per site (standard and premium pricing)
- Admin users (1 super admin + 3 site admins)
- Product categories (Bebidas, Snacks, Equipamiento, Alquiler)
- Sample products with pricing
- 3 membership plans (Basico, Premium, VIP)
- 5 sample clients with one Premium membership

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

apps/web/package.json

@@ -10,7 +10,8 @@
     "type-check": "tsc --noEmit",
     "db:generate": "prisma generate",
     "db:push": "prisma db push",
-    "db:studio": "prisma studio"
+    "db:studio": "prisma studio",
+    "db:seed": "tsx prisma/seed.ts"
   },
   "dependencies": {
     "@padel-pro/shared": "*",
@@ -42,6 +43,7 @@
     "postcss": "^8.4.35",
     "prisma": "^5.10.0",
     "tailwindcss": "^3.4.1",
+    "tsx": "^4.7.0",
     "typescript": "^5.3.3"
   }
 }