feat: Enhance logout functionality and routing in authentication system

- Integrate `useRouter` in `UserProfile.vue` and `useAuth.ts` to manage navigation after logout.
- Update `handleLogout` in `Navbar.vue` to reflect that redirection is now handled within the `auth.logout()` function.

src/composables/useAuth.ts

@@ -1,4 +1,5 @@
 import { ref, computed } from 'vue'
+import { useRouter } from 'vue-router'
 import { lnbitsAPI, type User, type LoginCredentials, type RegisterData } from '@/lib/api/lnbits'
 
 const currentUser = ref<User | null>(null)
@@ -6,6 +7,7 @@ const isLoading = ref(false)
 const error = ref<string | null>(null)
 
 export function useAuth() {
+  const router = useRouter()
   const isAuthenticated = computed(() => !!currentUser.value)
 
   /**
@@ -82,6 +84,8 @@ export function useAuth() {
     } finally {
       currentUser.value = null
       error.value = null
+      // Redirect to login page after logout
+      router.push('/login')
     }
   }