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.

src/components/TowerBackground.tsx

@@ -0,0 +1,11 @@
+export function TowerBackground() {
+  return (
+    <div className="absolute inset-0 bg-gradient-to-br from-[var(--primary)]/20 via-[var(--background)] to-[var(--accent)]/20">
+      {/* Effet de profondeur */}
+      <div className="absolute inset-0 bg-gradient-to-t from-black/20 via-transparent to-transparent"></div>
+      
+      {/* Effet de lumière */}
+      <div className="absolute inset-0 bg-gradient-to-br from-transparent via-[var(--primary)]/5 to-transparent"></div>
+    </div>
+  )
+}