feat(ccip): tunable match threshold, default 0.85 (#114)

Live data showed the v1 flat 0.75 cosine over-fired — ~64% of matched images got
3-10 character guesses dominated by the most-referenced characters (a 27-ref
character clears a low bar on many images). A sweep showed 0.85 collapses the
noise (noisy multi-matches 47→3) while keeping the confident single-character
matches.

- ml_settings.ccip_match_threshold (migration 0063, default 0.85); match_image
  reads it (override still accepted). DEFAULT_SIM_THRESHOLD fallback 0.75→0.85.
- Exposed in GET/PATCH /api/ml/settings (validated 0.5–0.999).
- Slider in the GPU agent card ("Character-match strictness") — tune live, no
  redeploy, same observe-and-tune loop as auto-apply.

Test: a ~0.9-cosine figure matches at 0.85, dropped at 0.95.

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

frontend/src/components/settings/GpuAgentCard.vue

@@ -60,6 +60,22 @@
       Enqueues every image that doesn't have a CCIP embedding yet. Nothing
       processes until the agent is running.
     </p>
+
+    <!-- Match strictness -->
+    <div class="fc-section-h mt-5 mb-1">Character-match strictness</div>
+    <div v-if="ml.settings" class="d-flex align-center" style="gap:12px">
+      <v-slider
+        v-model="threshold" :min="0.70" :max="0.95" :step="0.01"
+        color="accent" hide-details density="compact" class="flex-grow-1"
+        :loading="savingThreshold" @end="onSaveThreshold"
+      />
+      <span class="fc-q__n" style="font-size:16px">{{ threshold.toFixed(2) }}</span>
+    </div>
+    <p class="fc-muted text-caption mt-1 mb-0">
+      How close a figure must be (CCIP cosine) to suggest a character. Higher =
+      stricter — fewer but more confident matches. 0.85 recommended; below ~0.80
+      a heavily-tagged character starts matching everything.
+    </p>
   </MaintenanceTile>
 </template>
 
@@ -69,14 +85,18 @@ import { computed, onMounted, onUnmounted, ref } from 'vue'
 
 import MaintenanceTile from '../common/MaintenanceTile.vue'
 import { useGpuStore } from '../../stores/gpu.js'
+import { useMLStore } from '../../stores/ml.js'
 import { copyText } from '../../utils/clipboard.js'
 
 const store = useGpuStore()
+const ml = useMLStore()
 const loading = ref(true)
 const tokenValue = ref(null)
 const masked = ref(true)
 const rotating = ref(false)
 const backfilling = ref(false)
+const threshold = ref(0.85)
+const savingThreshold = ref(false)
 const queue = ref({ pending: 0, leased: 0, done: 0, error: 0 })
 let pollTimer = null
 
@@ -94,9 +114,27 @@ onMounted(async () => {
   }
   await refreshQueue()
   pollTimer = setInterval(() => { if (!document.hidden) refreshQueue() }, 5000)
+  try {
+    await ml.loadSettings()
+    if (ml.settings?.ccip_match_threshold != null) {
+      threshold.value = ml.settings.ccip_match_threshold
+    }
+  } catch { /* non-fatal */ }
 })
 onUnmounted(() => { if (pollTimer) clearInterval(pollTimer) })
 
+async function onSaveThreshold() {
+  savingThreshold.value = true
+  try {
+    await ml.patchSettings({ ccip_match_threshold: threshold.value })
+    toast({ text: `Match strictness set to ${threshold.value.toFixed(2)}`, type: 'success' })
+  } catch (e) {
+    toast({ text: `Could not save: ${e.message}`, type: 'error' })
+  } finally {
+    savingThreshold.value = false
+  }
+}
+
 async function refreshQueue() {
   try { queue.value = await store.status() } catch { /* non-fatal */ }
 }