chore: retire ml-backfill-daily beat + the spent purge-legacy action (operator-approved)

- ml-backfill-daily: the CPU tag_and_embed backfill raced the GPU agent's
  daily embed backfill for the same NULL-embedding images at ~100x the cost
  (B1 audit verdict, milestone #124). The backfill TASK stays — the manual
  /api/ml/backfill button remains the deliberate CPU fallback pending B3.
- purge-legacy: one-time IR-migration cleanup, dry-run verified 0 targets on
  the live library before removal (A2 audit, milestone #123). Fully retired
  per rule 22: tile, store action, route, service fn, tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/components/settings/TagMaintenanceCard.vue

@@ -42,53 +42,6 @@
     </div>
   </MaintenanceTile>
 
-  <MaintenanceTile
-    icon="mdi-tag-off"
-    title="Legacy migration tags"
-    blurb="Purge retired archive/post/artist + source:* tags."
-    destructive
-  >
-    <p class="fc-muted text-body-2 mb-3">
-      Purge legacy IR-migration tags FC no longer uses: retired/system
-      kinds (<code>archive</code>, <code>post</code>, <code>artist</code> — e.g.
-      <code>BlenderKnight:Hannah_BJ_Loops</code>) plus <code>source:*</code> tags
-      (ImageRepo's old <code>source</code> kind, migrated to <code>general</code>).
-      Provenance and artists are their own systems now, so these are pure noise.
-      Removes them from every image.
-    </p>
-
-    <v-btn
-      color="accent" variant="flat" rounded="pill"
-      prepend-icon="mdi-magnify"
-      :loading="loadingKindPreview"
-      class="mb-3"
-      @click="onKindPreview"
-    >Preview legacy tags</v-btn>
-
-    <div v-if="kindPreview">
-      <p class="text-body-2 mb-2">
-        <strong>{{ kindPreview.count }}</strong> legacy tag(s).
-        <span v-for="(n, k) in kindPreview.by_kind" :key="k" class="fc-muted">
-          {{ k }}: {{ n }}&nbsp;&nbsp;
-        </span>
-        <span v-for="(n, p) in kindPreview.by_prefix" :key="p" class="fc-muted">
-          {{ p }}: {{ n }}&nbsp;&nbsp;
-        </span>
-      </p>
-      <SampleNameGrid
-        v-if="kindPreview.sample_names?.length"
-        :names="kindPreview.sample_names" class="mb-3"
-      />
-      <v-btn
-        color="error" variant="flat" rounded="pill"
-        prepend-icon="mdi-delete-sweep"
-        :disabled="!kindPreview.count"
-        :loading="kindCommitting"
-        @click="onKindCommit"
-      >Delete {{ kindPreview.count }} legacy tag(s)</v-btn>
-    </div>
-  </MaintenanceTile>
-
   <MaintenanceTile
     icon="mdi-tag-multiple"
     title="Reset content tagging"
@@ -216,16 +169,6 @@ const {
   emptyPreview: (r) => ({ count: 0, sample_names: r.sample_names || [] }),
 })
 
-// Legacy migration-tag purge.
-const {
-  previewData: kindPreview, previewing: loadingKindPreview,
-  committing: kindCommitting, runPreview: onKindPreview, runCommit: onKindCommit,
-} = usePreviewCommit({
-  preview: () => store.purgeLegacyTags({ dryRun: true }),
-  commit: () => store.purgeLegacyTags({ dryRun: false }),
-  emptyPreview: { count: 0, by_kind: {}, by_prefix: {}, sample_names: [] },
-})
-
 // Reset content tagging (general + character).
 const {
   previewData: resetPreview, previewing: loadingResetPreview,

frontend/src/stores/admin.js

@@ -101,10 +101,6 @@ export const useAdminStore = defineStore('admin', () => {
     })
   }
 
-  function purgeLegacyTags(opts = {}) {
-    return _dryRunPost('/api/admin/tags/purge-legacy', opts)
-  }
-
   // Destructive: deletes ALL general + character tags so the operator can
   // re-tag from scratch via auto-suggest. fandom + series preserved.
   function resetContentTagging(opts = {}) {
@@ -154,7 +150,6 @@ export const useAdminStore = defineStore('admin', () => {
     pruneUnusedTags,
     pruneBarePosts,
     reconcileDuplicatePosts,
-    purgeLegacyTags,
     resetContentTagging,
     normalizeTags,
     pollTaskUntilDone,