test(web): add frontend unit test baseline (#5451)

web/test/setup.ts

@@ -0,0 +1,25 @@
+import { enableAutoUnmount } from '@vue/test-utils'
+import { afterAll, afterEach, vi } from 'vitest'
+
+const originalFetch = globalThis.fetch
+const blockedFetch = vi.fn(async () => {
+  throw new Error('Real network requests are disabled in unit tests')
+})
+
+globalThis.fetch = blockedFetch as typeof fetch
+
+afterEach(() => {
+  vi.restoreAllMocks()
+  vi.unstubAllGlobals()
+  vi.clearAllMocks()
+  globalThis.fetch = blockedFetch as typeof fetch
+  document.body.innerHTML = ''
+})
+
+// Vitest runs afterEach hooks in reverse registration order, so wrappers are
+// unmounted before the cleanup hook above clears the DOM.
+enableAutoUnmount(afterEach)
+
+afterAll(() => {
+  globalThis.fetch = originalFetch
+})