feat: add authentication support and user model

- Updated `env.example` to include NextAuth configuration for authentication.
- Added `next-auth` dependency to manage user sessions.
- Introduced `User` model in Prisma schema with fields for user details and password hashing.
- Integrated `AuthProvider` in layout for session management across the app.
- Enhanced `Header` component with `AuthButton` for user authentication controls.

package.json

@@ -26,9 +26,11 @@
     "@dnd-kit/sortable": "^10.0.0",
     "@dnd-kit/utilities": "^3.2.2",
     "@prisma/client": "^6.16.1",
+    "bcryptjs": "^3.0.2",
     "clsx": "^2.1.1",
     "date-fns": "^4.1.0",
     "next": "15.5.3",
+    "next-auth": "^4.24.11",
     "prisma": "^6.16.1",
     "react": "19.1.0",
     "react-dom": "19.1.0",
@@ -38,6 +40,7 @@
   "devDependencies": {
     "@eslint/eslintrc": "^3",
     "@tailwindcss/postcss": "^4",
+    "@types/bcryptjs": "^2.4.6",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",