feat(maintenance): re-extract archive attachments + link to post — #713 part 2

Existing PostAttachments that are actually archives (filed opaquely before the
magic-byte gate) need extracting retroactively. cleanup_service.
reextract_archive_attachments scans PostAttachments, magic-detects the archives,
and for each reconstructs the post's sidecar from the DB + re-runs attach_in_place
in a temp dir — so the members extract and re-link to the SAME post via
find_or_create_post (source_id + external_post_id). Idempotent (members dedupe by
sha256). Enqueues thumbnail+ML for new members.

Wired as a maintenance-queue Celery task (tasks/admin) + POST
/api/admin/maintenance/reextract-archives (202) + a "Re-extract archive
attachments" card in Settings → Maintenance.

Test: a zip stored under a mangled extension-less name extracts + links its
member to the post via ImageProvenance, and a second run is a no-op (idempotent).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/settings/ArchiveReextractCard.vue

@@ -0,0 +1,46 @@
+<template>
+  <!-- #713: re-extract PostAttachments that are really archives but were filed
+       opaquely before the magic-byte gate, and attach their images to the post. -->
+  <v-card>
+    <v-card-title>Re-extract archive attachments</v-card-title>
+    <v-card-text>
+      <p class="text-body-2 mb-3">
+        Some posts attached an archive (zip) whose images weren't extracted
+        because the downloaded file had no usable extension. This scans existing
+        attachments, extracts any that are really archives, and attaches their
+        images to the post. Idempotent — safe to run more than once.
+      </p>
+      <v-btn color="primary" rounded="pill" :loading="busy" @click="run">
+        <v-icon start>mdi-folder-zip-outline</v-icon> Re-extract archives now
+      </v-btn>
+      <span v-if="queued" class="ml-3 text-caption text-success">Queued ✓</span>
+      <QueueStatusBar queue="maintenance" queue-label="Maintenance" />
+    </v-card-text>
+  </v-card>
+</template>
+
+<script setup>
+import { ref } from 'vue'
+
+import { useApi } from '../../composables/useApi.js'
+import { toast } from '../../utils/toast.js'
+import QueueStatusBar from './QueueStatusBar.vue'
+
+const api = useApi()
+const busy = ref(false)
+const queued = ref(false)
+
+async function run () {
+  busy.value = true
+  queued.value = false
+  try {
+    await api.post('/api/admin/maintenance/reextract-archives')
+    queued.value = true
+    toast({ text: 'Archive re-extract queued', type: 'success' })
+  } catch (e) {
+    toast({ text: e?.body?.detail || e?.message || 'Failed to queue', type: 'error' })
+  } finally {
+    busy.value = false
+  }
+}
+</script>

frontend/src/components/settings/MaintenancePanel.vue

@@ -15,6 +15,7 @@
     <AllowlistTable class="mt-4" />
     <AliasTable class="mt-4" />
     <DbMaintenanceCard class="mt-6" />
+    <ArchiveReextractCard class="mt-6" />
     <BackupCard class="mt-6" />
     <!-- TagMaintenanceCard moved to Cleanup tab (v26.05.25.7) — it
          operates on the existing library which fits the Cleanup-tab
@@ -33,6 +34,7 @@ import MLThresholdSliders from './MLThresholdSliders.vue'
 import AllowlistTable from './AllowlistTable.vue'
 import AliasTable from './AliasTable.vue'
 import DbMaintenanceCard from './DbMaintenanceCard.vue'
+import ArchiveReextractCard from './ArchiveReextractCard.vue'
 import BackupCard from './BackupCard.vue'
 import { useSystemActivityStore } from '../../stores/systemActivity.js'