Task 10.3: Add "Forgot password?" link with toast and "Sign up" link to login page

- Install sonner for toast notifications
- Add handleForgotPassword function that shows "Not yet available" toast
- Add "Forgot password?" link next to password label
- Verify "Sign up" link to /register exists
- Add Toaster component to public layout
- Mark task 10.3 as [x] in tasks.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -33,6 +33,7 @@
     "pg": "^8.13.1",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",
+    "sonner": "^2.0.7",
     "tailwind-merge": "^3.4.0",
     "zod": "^4.3.6"
   },