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/postCard.spec.js

@@ -0,0 +1,26 @@
+// @vitest-environment happy-dom
+import { describe, it, expect } from 'vitest'
+
+import PostCard from '../../src/components/posts/PostCard.vue'
+import { freshPinia, mountComponent } from '../support/mountComponent.js'
+
+describe('PostCard', () => {
+  it('renders the HTML-stripped title and the artist', () => {
+    const pinia = freshPinia()
+    const now = new Date().toISOString()
+    const post = {
+      id: 1, external_post_id: 'P1',
+      post_title: '<strong>Hello World</strong>',
+      post_url: 'https://x/1', post_date: now, downloaded_at: now,
+      description_plain: 'a description',
+      artist: { id: 1, name: 'Sabu', slug: 'sabu' },
+      source: { id: 1, platform: 'subscribestar' },
+      thumbnails: [], thumbnails_more: 0, attachments: [],
+    }
+    const w = mountComponent(PostCard, { props: { post }, pinia })
+    const t = w.text()
+    expect(t).toContain('Hello World')   // plain title
+    expect(t).not.toContain('<strong>')  // tags stripped
+    expect(t).toContain('Sabu')          // artist (RouterLink slot)
+  })
+})