refactor(ml): remove the dead per-tag centroid subsystem (#1189)

The v2 pivot replaced per-tag SigLIP centroids with learned heads + CCIP.
Centroids were still recomputed (on every tag merge + a daily beat) but NOTHING
read them — suggestions come from heads+CCIP and apply_allowlist_tags applies
via Camie predictions, not centroids. Pure dead wiring; remove it.

Removed: CentroidService, recompute_centroid/recompute_centroids tasks, the
daily beat, POST /api/ml/recompute-centroids, the recompute-on-merge trigger,
the tag_reference_embedding table + model, the centroid_similarity_threshold +
min_reference_images settings (migration 0066), the CentroidRecomputeCard +
its store action + MaintenancePanel tile, and the centroid slider in
MLThresholdSliders. _keep_as_alias drops its vestigial has-centroid branch (the
allowlist branch already covers "could re-emit"); tag merge no longer clears a
table that no longer exists.

NOT touched (still live, parallel to heads): the Camie tagger, ImagePrediction,
and the allowlist bulk-apply — accepting a suggestion still allowlists + applies
it across the library. The tag-eval "centroid" baseline metric is unrelated
(in-memory) and stays. (image_record.centroid_scores JSON column also remains —
separate legacy field, its own micro-cleanup.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

frontend/src/components/settings/CentroidRecomputeCard.vue

@@ -1,36 +0,0 @@
-<template>
-  <MaintenanceTile
-    icon="mdi-vector-triangle"
-    title="Tag centroids"
-    blurb="Rebuild SigLIP centroids for similarity suggestions."
-    :open="busy"
-  >
-      <p class="text-body-2 mb-3">
-        Rebuild the per-tag SigLIP centroids that power similarity-based
-        suggestions. Runs nightly automatically; trigger manually after a
-        large tagging session.
-      </p>
-      <v-btn color="primary" rounded="pill" :loading="busy" @click="run">
-        <v-icon start>mdi-vector-triangle</v-icon> Recompute centroids
-      </v-btn>
-      <span v-if="done" class="ml-3 text-caption">Enqueued.</span>
-      <QueueStatusBar queue="ml" queue-label="ML" />
-  </MaintenanceTile>
-</template>
-
-<script setup>
-import { toast } from '../../utils/toast.js'
-import { ref } from 'vue'
-import { useMLStore } from '../../stores/ml.js'
-import MaintenanceTile from '../common/MaintenanceTile.vue'
-import QueueStatusBar from './QueueStatusBar.vue'
-const store = useMLStore()
-const busy = ref(false)
-const done = ref(false)
-async function run() {
-  busy.value = true
-  try { await store.triggerRecomputeCentroids(); done.value = true }
-  catch (e) { toast({ text: e.message, type: 'error' }) }
-  finally { busy.value = false }
-}
-</script>

frontend/src/components/settings/MLThresholdSliders.vue

@@ -28,8 +28,7 @@
           <div class="text-caption fc-muted mt-1">
             Tagger predictions below this confidence aren't stored — raising it
             keeps the image library lean. Suggestions can't be shown below the
-            floor; lower-confidence tags you actually want still surface through
-            the learned centroid path.
+            floor.
           </div>
         </v-col>
       </v-row>
@@ -84,8 +83,7 @@ const store = useMLStore()
 // tagger store floor (nothing below the floor is stored to surface).
 const fields = [
   { key: 'suggestion_threshold_character', label: 'Character', floorMin: true },
-  { key: 'suggestion_threshold_general', label: 'General', floorMin: true },
-  { key: 'centroid_similarity_threshold', label: 'Centroid similarity' }
+  { key: 'suggestion_threshold_general', label: 'General', floorMin: true }
 ]
 const local = reactive({})
 watch(() => store.settings, (s) => { if (s) Object.assign(local, s) }, { immediate: true })

frontend/src/components/settings/MaintenancePanel.vue

@@ -1,9 +1,8 @@
 <template>
   <div class="fc-maint">
     <p class="fc-muted text-body-2 mb-5">
-      One-off backfills, tagging config and storage tools. The ML backfill and
-      centroid recompute also run nightly; the allowlist auto-applies accepted
-      tags. Click a tile to open it.
+      One-off backfills, tagging config and storage tools. The ML backfill runs
+      nightly; the allowlist auto-applies accepted tags. Click a tile to open it.
     </p>
 
     <section class="fc-section">
@@ -11,7 +10,6 @@
       <p class="fc-section__hint">Re-run tagging, thumbnails, extraction and DB upkeep.</p>
       <div class="fc-tile-grid">
         <MLBackfillCard />
-        <CentroidRecomputeCard />
         <ThumbnailBackfillCard />
         <ArchiveReextractCard />
         <MissingFileRepairCard />
@@ -48,7 +46,6 @@
 import { onMounted, onUnmounted } from 'vue'
 
 import MLBackfillCard from './MLBackfillCard.vue'
-import CentroidRecomputeCard from './CentroidRecomputeCard.vue'
 import ThumbnailBackfillCard from './ThumbnailBackfillCard.vue'
 import ArchiveReextractCard from './ArchiveReextractCard.vue'
 import MissingFileRepairCard from './MissingFileRepairCard.vue'