feat(07-05): DocumentCard classification_failed badge + Re-analyze button + Vitest coverage

- Add red "Classification failed" pill badge when doc.status === 'classification_failed'
- Re-analyze button calls classifyDocument(doc.id) via @click.stop, emits 'reclassified'
- Spinner text "Re-analyzing…" while in flight; resets after 500ms (via setTimeout)
- Existing is_shared badge block preserved unchanged
- Create frontend/tests/DocumentCard.spec.js: 4 Vitest tests covering badge render,
  no-badge for ready/processing, and reanalyze() calling classifyDocument + emit
- 131 frontend tests pass, build exits 0 (D-11 frontend coverage per CLAUDE.md)

frontend/src/components/documents/DocumentCard.vue

@@ -31,6 +31,19 @@
         <div v-if="doc.is_shared" class="mt-2">
           <span class="bg-indigo-50 text-indigo-600 text-xs font-medium px-2 py-1 rounded-full">Shared</span>
         </div>
+
+        <!-- Classification failed badge + Re-analyze button -->
+        <div v-if="doc.status === 'classification_failed'" class="mt-2 flex items-center gap-2">
+          <span class="bg-red-50 text-red-600 text-xs font-medium px-2 py-1 rounded-full">Classification failed</span>
+          <button
+            @click.stop="reanalyze"
+            :disabled="reanalyzing"
+            class="text-xs text-indigo-600 hover:text-indigo-700 font-semibold disabled:opacity-50"
+          >
+            <span v-if="reanalyzing">Re-analyzing…</span>
+            <span v-else>Re-analyze</span>
+          </button>
+        </div>
       </div>
 
       <!-- Action buttons (hover-reveal) -->
@@ -94,7 +107,7 @@
 import { ref, computed, onMounted, onUnmounted } from 'vue'
 import { useTopicsStore } from '../../stores/topics.js'
 import { useFoldersStore } from '../../stores/folders.js'
-import { moveDocument } from '../../api/client.js'
+import { moveDocument, classifyDocument } from '../../api/client.js'
 import TopicBadge from '../topics/TopicBadge.vue'
 import ShareModal from '../sharing/ShareModal.vue'
 import { formatDate, formatSize } from '../../utils/formatters.js'
@@ -103,10 +116,13 @@ const props = defineProps({
   doc: Object,
 })
 
+const emit = defineEmits(['reclassified'])
+
 const topicsStore = useTopicsStore()
 const foldersStore = useFoldersStore()
 const showShareModal = ref(false)
 const showFolderPicker = ref(false)
+const reanalyzing = ref(false)
 
 const allFolders = computed(() => foldersStore.rootFolders)
 
@@ -138,4 +154,16 @@ function topicColor(name) {
   return topicsStore.topics.find(t => t.name === name)?.color ?? '#6366f1'
 }
 
+async function reanalyze() {
+  reanalyzing.value = true
+  try {
+    await classifyDocument(props.doc.id)
+    emit('reclassified', props.doc.id)
+  } catch (e) {
+    console.error('Re-analyze failed:', e.message)
+  } finally {
+    setTimeout(() => { reanalyzing.value = false }, 500)
+  }
+}
+
 </script>