feat: add duplicate email detection via auth hook with fallback

- Add before-user-created hook function for server-side duplicate email detection
- Implement fallback detection using identities array check (Supabase limitation)
- Update signUpWithPassword to detect duplicate emails via hook errors or empty identities
- Add error handling in login page to show duplicate email errors and auto-switch to login mode
- Add auth hook setup documentation and test scripts
- Add password reset and update password flows
- Add email templates for signup confirmation and password reset

package.json

@@ -7,7 +7,8 @@
     "build": "next build --webpack",
     "start": "next start",
     "lint": "eslint",
-    "types:generate": "npx supabase gen types typescript --project-id dqugbrpwtisgyxscpefg > lib/supabase/types.ts"
+    "types:generate": "npx supabase gen types typescript --project-id dqugbrpwtisgyxscpefg > lib/supabase/types.ts",
+    "setup:auth-hook": "tsx scripts/setup-auth-hook.ts"
   },
   "dependencies": {
     "@radix-ui/react-icons": "^1.3.2",