feat(frontend): add branded not-found page

frontend/app/error.test.ts

@@ -0,0 +1,21 @@
+import { mount } from '@vue/test-utils'
+import { describe, expect, it } from 'vitest'
+
+import ErrorPage from './error.vue'
+
+describe('ErrorPage', () => {
+  it('renders a branded not-found page with a way home', () => {
+    const wrapper = mount(ErrorPage, {
+      props: {
+        error: {
+          statusCode: 404,
+          statusMessage: 'Page not found',
+        },
+      },
+    })
+
+    expect(wrapper.get('h1').text()).toBe('صفحه پیدا نشد')
+    expect(wrapper.get('a').attributes('href')).toBe('/')
+    expect(wrapper.get('[role="img"]').attributes('aria-label')).toBe('زرین‌پال')
+  })
+})