feat(provenance+tags): collapse provenance descriptions; purge retired-kind tags

Operator-flagged 2026-05-28, two asks.

**1. Provenance posts ate the panel.** Each post card rendered its full
description (180px scroll box) inline, so a few posts pushed everything
else off-screen. ProvenancePanel now collapses the description by
default behind a per-post "Show description ▾ / Hide ▴" toggle (state
keyed by provenance_id, reset when the viewed image changes). Cards stay
compact — platform/date/title/meta/actions — and the operator expands
only the descriptions they want.

**2. Purge tags of retired/system kinds.** The IR migration left
`archive`/`post`/`artist`-kind tags (e.g. `BlenderKnight:Hannah_BJ_Loops`)
that FC no longer creates — the tag input only makes
character/fandom/series/general, and provenance + artists are their own
systems now. (meta/rating were already hard-deleted by alembic 0023.)

- cleanup_service.purge_tags_by_kind(kinds=PURGEABLE_TAG_KINDS) — counts
  (dry_run) or deletes tags whose kind ∈ (archive, post, artist).
  CASCADE clears the image_tag / alias / allowlist / etc. rows.
- POST /api/admin/tags/purge-retired-kinds (Tier-A, dry-run preview
  returns per-kind counts + sample names — the preview IS the
  verification of exactly what'll be deleted before committing).
- Tag Maintenance card gets a second section: "Preview retired-kind
  tags" → per-kind breakdown + sample → "Delete N retired-kind tag(s)".

Tests: dry-run counts by kind (general survives), commit deletes only
the retired kinds (general + character survive, retired count → 0).

NOTE: a dry-run preview will show exactly which kinds/counts are
present. If the operator's noisy tags turn out to be `general` (e.g. an
IR `source:patreon` that fell back to general during migration), they
won't be caught by the kind purge — the preview makes that visible so
we can decide on a name-based pass separately.

frontend/src/components/settings/TagMaintenanceCard.vue

@@ -44,6 +44,46 @@
           @click="onCommit"
         >Delete {{ preview.count }} unused tag(s)</v-btn>
       </div>
+
+      <v-divider class="my-5" />
+
+      <p class="fc-muted text-body-2 mb-4">
+        Purge tags with retired/system kinds FC no longer uses
+        (<code>archive</code>, <code>post</code>, <code>artist</code>) —
+        IR-migration leftovers like
+        <code>BlenderKnight:Hannah_BJ_Loops</code>. Provenance and
+        artists are their own systems now, so these tag rows 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 retired-kind tags</v-btn>
+
+      <div v-if="kindPreview">
+        <p class="text-body-2 mb-2">
+          <strong>{{ kindPreview.count }}</strong> tag(s) of retired kinds.
+          <span v-for="(n, k) in kindPreview.by_kind" :key="k" class="fc-muted">
+            {{ k }}: {{ n }}&nbsp;&nbsp;
+          </span>
+        </p>
+        <div v-if="kindPreview.sample_names?.length" class="fc-name-grid mb-3">
+          <span v-for="n in kindPreview.sample_names" :key="n" class="fc-name">
+            {{ n }}
+          </span>
+        </div>
+        <v-btn
+          color="error" variant="flat" rounded="pill"
+          prepend-icon="mdi-delete-sweep"
+          :disabled="!kindPreview.count"
+          :loading="kindCommitting"
+          @click="onKindCommit"
+        >Delete {{ kindPreview.count }} retired-kind tag(s)</v-btn>
+      </div>
     </v-card-text>
   </v-card>
 </template>
@@ -57,6 +97,9 @@ const store = useAdminStore()
 const preview = ref(null)
 const loadingPreview = ref(false)
 const committing = ref(false)
+const kindPreview = ref(null)
+const loadingKindPreview = ref(false)
+const kindCommitting = ref(false)
 
 async function onPreview() {
   loadingPreview.value = true
@@ -76,6 +119,25 @@ async function onCommit() {
     committing.value = false
   }
 }
+
+async function onKindPreview() {
+  loadingKindPreview.value = true
+  try {
+    kindPreview.value = await store.purgeRetiredKindTags({ dryRun: true })
+  } finally {
+    loadingKindPreview.value = false
+  }
+}
+
+async function onKindCommit() {
+  kindCommitting.value = true
+  try {
+    await store.purgeRetiredKindTags({ dryRun: false })
+    kindPreview.value = { count: 0, by_kind: {}, sample_names: [] }
+  } finally {
+    kindCommitting.value = false
+  }
+}
 </script>
 
 <style scoped>