test(I2): vitest component smoke tests for high-risk UI

Adds @vue/test-utils + happy-dom and mounts CredentialCard, DownloadEventRow,
PostCard, ActiveDownloadsPanel, QueueStatusBar, asserting they render without
throwing and surface key content — catching the dead-binding / render-error
class (e.g. the last_verified_at regression, guarded explicitly). Vuetify
components are left unresolved (Vue renders unknown elements + slots), so no
Vuetify-plugin setup is needed; only RouterLink is stubbed. Per-file
happy-dom env via docblock keeps the existing node-env specs untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/test/components/downloadEventRow.spec.js

@@ -0,0 +1,21 @@
+// @vitest-environment happy-dom
+import { describe, it, expect } from 'vitest'
+
+import DownloadEventRow from '../../src/components/downloads/DownloadEventRow.vue'
+import { freshPinia, mountComponent } from '../support/mountComponent.js'
+
+describe('DownloadEventRow', () => {
+  it('renders the artist and the mapped status label', () => {
+    const pinia = freshPinia()
+    const now = new Date().toISOString()
+    const event = {
+      id: 1, status: 'ok', started_at: now, finished_at: now,
+      platform: 'patreon', artist_name: 'Alice',
+      files_count: 3, bytes_downloaded: 1000, error: null, summary: {},
+    }
+    const w = mountComponent(DownloadEventRow, { props: { event }, pinia })
+    const t = w.text()
+    expect(t).toContain('Alice')
+    expect(t).toContain('Completed') // downloadStatusLabel('ok')
+  })
+})