feat: Settings can re-download the Discord images the None naming broke (3999)

The operator chose a clean re-download over relinking in place. The ~1,600 broken files can't be relinked reliably: their message ids are gone, and their sidecars collided.

Settings → Maintenance → "Repair Discord downloads" previews, then applies:
- Deletes every image whose path is `…/discord/None/<8 digits>_None_…`. Both the folder and the name are required, because that pair is only what the bug produced. It reuses cleanup_service.delete_images for the record and file deletes.
- Sweeps the leftover collided sidecars from those folders and removes the emptied folders.
- Only then clears gallery-dl's archive rows `discord%`, excluding `discordasset_%`. Upstream keys message attachments as `discord{message_id}_{num}`. Since the broken files lost their message ids, per-source forgetting is impossible. Every pre-fix Discord download is broken, and files fetched after the fix still exist on disk, so gallery-dl's `skip` won't re-fetch them.
- Arms a fresh backfill on every Discord source.

The apply defaults to preview at both the route and the task, runs on maintenance_long, and is never on a beat. The card uses the confirm-dialog pattern of AttachmentReclaimCard.

Supporting refactors, with no behaviour change:
- gallery_dl.archive_path() is the single definition of the archive location.
- source_service.arm_backfill() is the mutation start_backfill already did, now shared with the sync repair.

Tests (tests/test_discord_repair.py):
- The archive clear leaves other platforms and Discord assets alone, and counting mutates nothing.
- Case-twin artist folders are both found.
- The folder sweep works.
- An integration run shows only the broken image goes. A correctly named Discord file and a `None` folder under Patreon survive, and only Discord sources are re-armed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SHQB1YukL3VyvMK8rcbmV9

frontend/src/components/settings/DiscordRepairCard.vue

@@ -0,0 +1,118 @@
+<template>
+  <!-- #3999: Discord downloads made before the naming fix landed in a `None`
+       folder with no post and a download-time date. This re-downloads them
+       cleanly. Preview first; the apply deletes files. -->
+  <MaintenanceTile
+    icon="mdi-download-off-outline"
+    title="Repair Discord downloads"
+    blurb="Re-download Discord images that were saved with no post and the wrong date."
+    destructive
+    :open="applying || previewing"
+  >
+    <p class="text-body-2 mb-3">
+      Before the naming fix, every Discord download was saved into a folder
+      called <code>None</code>. Those images never got a post, so they show the
+      time Curator downloaded them rather than when they were posted.
+      <strong>Apply</strong> deletes those images, clears Discord from the
+      download history, and starts a fresh backfill of every Discord source so
+      they come back with their posts and dates. Tags you added by hand to those
+      images are lost. Nothing outside a Discord <code>None</code> folder is
+      touched.
+    </p>
+
+    <div class="d-flex align-center flex-wrap" style="gap: 12px;">
+      <v-btn
+        color="primary" variant="tonal" rounded="pill"
+        :loading="previewing" :disabled="applying" @click="preview"
+      >
+        <v-icon start>mdi-magnify</v-icon> Preview
+      </v-btn>
+      <v-btn
+        color="error" rounded="pill"
+        :loading="applying"
+        :disabled="previewing || !canApply"
+        @click="confirmOpen = true"
+      >
+        <v-icon start>mdi-download-off-outline</v-icon> Apply
+      </v-btn>
+    </div>
+
+    <v-alert
+      v-if="summary" :type="summaryType" variant="tonal" class="mt-4"
+      density="comfortable"
+    >
+      <span v-if="applied">
+        Deleted {{ summary.images_deleted }} image(s) and cleared
+        {{ summary.archive_entries }} Discord download record(s). Backfills
+        started on {{ summary.backfills_started }} Discord source(s).
+      </span>
+      <span v-else-if="hasWork">
+        {{ summary.images }} broken image(s) ({{ humanBytes(summary.bytes) }})
+        across {{ summary.directories }} folder(s), and
+        {{ summary.archive_entries }} Discord download record(s) to clear.
+        {{ summary.sources }} Discord source(s) will backfill again.
+      </span>
+      <span v-else>Nothing to repair — no broken Discord downloads found.</span>
+
+      <div v-if="applied && summary.files_failed" class="mt-1 text-caption">
+        {{ summary.files_failed }} file(s) could not be removed — see the worker log.
+      </div>
+      <div v-if="applied && summary.remaining" class="mt-1 text-caption">
+        {{ summary.remaining }} broken image(s) are still present. Run it again.
+      </div>
+    </v-alert>
+
+    <QueueStatusBar queue="maintenance_long" queue-label="Maintenance" />
+
+    <v-dialog v-model="confirmOpen" max-width="440">
+      <v-card>
+        <v-card-title>Repair Discord downloads?</v-card-title>
+        <v-card-text class="text-body-2">
+          This permanently deletes <strong>{{ summary?.images ?? 0 }}</strong>
+          Discord image(s) ({{ humanBytes(summary?.bytes) }}) and re-downloads
+          them from Discord with their posts and dates. Any tags you added to
+          those images by hand will not come back.
+        </v-card-text>
+        <v-card-actions>
+          <v-spacer />
+          <v-btn variant="text" @click="confirmOpen = false">Cancel</v-btn>
+          <v-btn color="error" @click="apply">Repair</v-btn>
+        </v-card-actions>
+      </v-card>
+    </v-dialog>
+  </MaintenanceTile>
+</template>
+
+<script setup>
+import { computed, ref } from 'vue'
+
+import { useMaintenanceTask } from '../../composables/useMaintenanceTask.js'
+import { humanBytes } from '../../utils/bytes.js'
+import MaintenanceTile from '../common/MaintenanceTile.vue'
+import QueueStatusBar from './QueueStatusBar.vue'
+
+const confirmOpen = ref(false)
+
+const { previewing, applying, summary, applied, preview, apply: applyTask } = useMaintenanceTask({
+  endpoint: '/api/admin/maintenance/repair-discord-downloads',
+  storageKey: 'fc.maint.repairDiscordDownloads',
+  appliedToast: 'Discord downloads cleared — backfills started',
+})
+
+// The archive count matters too: files could already be gone while gallery-dl
+// still believes it has them, which would stop the backfill re-fetching.
+const hasWork = computed(
+  () => !!summary.value && (summary.value.images > 0 || summary.value.archive_entries > 0),
+)
+const canApply = computed(() => hasWork.value && !applied.value)
+const summaryType = computed(() => {
+  if (applied.value) return 'success'
+  return hasWork.value ? 'info' : 'success'
+})
+
+// The confirm dialog gates the destructive apply; close it, then run.
+function apply () {
+  confirmOpen.value = false
+  applyTask()
+}
+</script>

frontend/src/components/settings/MaintenancePanel.vue

@@ -15,6 +15,7 @@
         <ImportFiltersForm />
         <TranslationCard />
         <DiscordGroupingCard />
+        <DiscordRepairCard />
         <PostAssociationsCard />
         <MembershipRosterCard />
         <MembershipSuggestionsCard />
@@ -85,6 +86,7 @@ import VideoEmbeddingCard from './VideoEmbeddingCard.vue'
 import CropProposersCard from './CropProposersCard.vue'
 import HeadsCard from './HeadsCard.vue'
 import DiscordGroupingCard from './DiscordGroupingCard.vue'
+import DiscordRepairCard from './DiscordRepairCard.vue'
 import MembershipRosterCard from './MembershipRosterCard.vue'
 import MembershipSuggestionsCard from './MembershipSuggestionsCard.vue'
 import PostAssociationsCard from './PostAssociationsCard.vue'