feat: #399 form validation and error handling across all forms

- Add react-hook-form, zod, @hookform/resolvers dependencies
- Create frontend/src/lib/validations.ts with Zod schemas for
  login, signup, and contact forms
- Create frontend/src/component/FormField.tsx with reusable components:
  FormInput, FormTextarea, FormSelect, FormLabel, FieldError,
  FieldSuccess, SubmitButton, FormSuccessBanner, FormErrorBanner
- Refactor login/page.tsx: inline validation, loading state, success/error banners
- Refactor signin/page.tsx: inline validation, password strength meter,
  confirm password match, loading state, success/error banners
- Refactor contact/page.tsx: replace manual validate() with Zod schema,
  use reusable form components throughout

Author: amankoli09

frontend/package-lock.json

@@ -10,6 +10,7 @@
   },
   "dependencies": {
     "@headlessui/react": "^2.2.4",
+    "@hookform/resolvers": "^5.2.2",
     "@radix-ui/react-progress": "^1.1.7",
     "@radix-ui/react-slot": "^1.2.3",
     "@radix-ui/react-tabs": "^1.1.12",
@@ -22,9 +23,11 @@
     "next": "^16.1.6",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",
+    "react-hook-form": "^7.72.0",
     "react-icons": "^5.6.0",
     "tailwind-merge": "^3.3.0",
-    "three": "^0.182.0"
+    "three": "^0.182.0",
+    "zod": "^4.3.6"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",