feat(logout): add logout button and logic with error handling

- Added a logout button in the header.
- added `useLogoutService` to call the `/logout` endpoint.
- Added error handling with `useErrorToast` to display error messages on logout failure.
- Redirects user to the home page on successful logout.
- adds unit tests

RISDEV-5806

frontend/src/components/controls/RisNavbar.spec.ts

@@ -1,8 +1,28 @@
-import { render, screen } from "@testing-library/vue"
-import { describe, expect, it } from "vitest"
+import { render, screen, fireEvent } from "@testing-library/vue"
+import { describe, expect, it, vi } from "vitest"
 import RisNavbar from "./RisNavbar.vue"
 import { createRouter, createWebHashHistory } from "vue-router"
 
+const add = vi.fn()
+vi.mock("primevue/usetoast", () => {
+  return {
+    useToast: () => ({
+      add: add,
+    }),
+  }
+})
+
+const pushMock = vi.fn()
+vi.mock("vue-router", async () => {
+  const actual = await vi.importActual("vue-router")
+  return {
+    ...actual,
+    useRouter: () => ({
+      push: pushMock,
+    }),
+  }
+})
+
 describe("risNavbar", () => {
   it("should show 'Rechtsinformationen' and 'des Bundes'", () => {
     const router = createRouter({
@@ -14,4 +34,28 @@ describe("risNavbar", () => {
     expect(screen.getByText("Rechtsinformationen")).toBeInTheDocument()
     expect(screen.getByText("des Bundes")).toBeInTheDocument()
   })
+
+  it("should render the logout button", () => {
+    const router = createRouter({
+      history: createWebHashHistory(),
+      routes: [{ name: "Home", path: "/", component: () => {} }],
+    })
+
+    render(RisNavbar, { global: { plugins: [router] } })
+    expect(screen.getByRole("button", { name: "Logout" })).toBeInTheDocument()
+  })
+
+  it("should redirect to Home on logout button click", async () => {
+    const router = createRouter({
+      history: createWebHashHistory(),
+      routes: [{ name: "Home", path: "/", component: () => {} }],
+    })
+
+    render(RisNavbar, { global: { plugins: [router] } })
+
+    const logoutButton = screen.getByRole("button", { name: "Logout" })
+    await fireEvent.click(logoutButton)
+
+    expect(pushMock).toHaveBeenCalledWith({ name: "Home" })
+  })
 })

frontend/src/components/controls/RisNavbar.vue

@@ -1,6 +1,22 @@
 <script setup lang="ts">
 import neurisLogo from "@/assets/neuRIS-logo.svg"
-import { RouterLink } from "vue-router"
+import { RouterLink, useRouter } from "vue-router"
+import Button from "primevue/button"
+import { useLogoutService } from "@/services/logoutService"
+import { useErrorToast } from "@/lib/errorToast"
+
+const { addErrorToast } = useErrorToast()
+const router = useRouter()
+
+async function handleLogout() {
+  const { error } = useLogoutService()
+
+  if (error?.value) {
+    addErrorToast(error.value)
+  } else {
+    await router.push({ name: "Home" })
+  }
+}
 </script>
 
 <template>
@@ -14,5 +30,6 @@ import { RouterLink } from "vue-router"
         <span class="ris-label3-regular block">des Bundes</span>
       </span>
     </RouterLink>
+    <Button label="Logout" severity="primary" @click="handleLogout"></Button>
   </nav>
 </template>

frontend/src/services/logoutService.spec.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect, vi, beforeEach } from "vitest"
+
+describe("logoutService", () => {
+  beforeEach(() => {
+    vi.resetModules()
+    vi.resetAllMocks()
+  })
+
+  it("calls the /logout endpoint with POST method", async () => {
+    const useFetchMock = {
+      error: { value: null },
+      isFetching: { value: false },
+    }
+
+    vi.doMock("@/services/apiService", () => ({
+      useApiFetch: vi.fn().mockReturnValue(useFetchMock),
+    }))
+
+    const { useLogoutService } = await import("@/services/logoutService")
+
+    const result = useLogoutService()
+
+    expect(result.error.value).toBe(null)
+    expect(result.isFetching.value).toBe(false)
+
+    const { useApiFetch } = await import("@/services/apiService")
+    expect(useApiFetch).toHaveBeenCalledWith("/logout", {
+      method: "POST",
+    })
+  })
+})

frontend/src/services/logoutService.ts

@@ -0,0 +1,13 @@
+import { UseFetchReturn } from "@vueuse/core"
+import { useApiFetch } from "@/services/apiService"
+
+/**
+ * Service to log out the user.
+ *
+ * Calls the backend `/logout` endpoint.
+ */
+export function useLogoutService(): UseFetchReturn<void> {
+  return useApiFetch("/logout", {
+    method: "POST",
+  })
+}