fix(audit-g5): centroid version DB-as-truth + modal as overlay

Closes the last two findings from the 2026-06-02 audit (G5.1 + G5.4).

G5.1 — Centroid version no longer drifts:

CentroidService now reads MLSettings.embedder_model_version (the DB
row tag_and_embed already writes from) for both the centroid model-
version stamp and the drift-detection comparison. Previously the
centroid sites imported MODEL_VERSION from env, so the version stamped
on centroids could disagree with the version stamped on the embeddings
they were built from. By construction those now match, so list_drifted
won't silently miss the env-vs-DB drift case.

embedder.py keeps MODEL_VERSION as an env-driven constant for the
actual model loader — that's a different concern (which weights are
loaded) from the version-stamp that gets persisted alongside data.

G5.4 — Modal is a Pinia-only overlay:

The previous URL↔modal sync in GalleryView and ArtistGalleryTab
leaked the modal across route changes (RouterLink to /artist/<slug>
left the modal mounted on top of the new route) and re-opened it
on history back/forward with stale ?image=N entries.

Now: openImage() just calls modal.open(id) — no URL push.
GalleryView's dead closeImage helper is deleted. A route.name
watcher in App.vue closes the modal whenever the route changes,
which auto-fixes RouterLink-in-modal and back/forward.

Backward-compat: ?image=N is still honored on initial mount as a
one-shot deep-link opener, then router.replace strips the query so
the URL doesn't re-trigger and no extra history entry is added.
Existing bookmarks / shared URLs keep working; new opens stay
Pinia-only.

frontend/src/components/artist/ArtistGalleryTab.vue

@@ -11,7 +11,7 @@
 </template>
 
 <script setup>
-import { onMounted, watch } from 'vue'
+import { onMounted } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 
 import { useArtistStore } from '../../stores/artist.js'
@@ -28,18 +28,20 @@ const route = useRoute()
 const router = useRouter()
 
 onMounted(() => {
+  // Audit 2026-06-02: same overlay treatment as GalleryView —
+  // honor `?image=N` once for backward-compat, then strip the
+  // query and let the modal live in Pinia-only state.
   const initial = parseInt(route.query.image, 10)
-  if (!isNaN(initial)) modal.open(initial)
-})
-
-watch(() => route.query.image, (q) => {
-  const id = parseInt(q, 10)
-  if (!isNaN(id) && id !== modal.currentImageId) modal.open(id)
-  else if (isNaN(id) && modal.currentImageId !== null) modal.close()
+  if (!isNaN(initial)) {
+    modal.open(initial)
+    const q = { ...route.query }
+    delete q.image
+    router.replace({ query: q })
+  }
 })
 
 function openImage (id) {
-  router.push({ query: { ...route.query, image: id } })
+  modal.open(id)
 }
 </script>