Add Stripe subscription system and n8n chat webhook

- Add Stripe SDK and subscription management
- Create checkout, webhook, and portal API routes
- Add pricing page with plan cards
- Create subscriptions table in Supabase
- Update database types for subscriptions
- Configure n8n webhook for AI chat responses

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

package.json

@@ -27,6 +27,7 @@
     "react": "19.2.1",
     "react-dom": "19.2.1",
     "sonner": "^2.0.7",
+    "stripe": "^20.0.0",
     "tailwind-merge": "^3.4.0"
   },
   "devDependencies": {