feat(artist): editable display name + rename surface; drop name-uniqueness (#130 step 1)

First step of decoupling artist identity/storage/display. migration 0077 drops
uq_artist_name so the display name is free text (two genuinely different creators
can share a name); the slug stays the immutable, unique storage/identity key (the
on-disk path component — untouched, so nothing moves). ArtistService.rename +
PATCH /api/artists/<id> change the name ONLY. Frontend: inline pencil-edit on the
artist header (mirrors TagCard), slug/route unaffected so no navigation. Fixes the
operator's 'no surface to rename an artist' + the name-collision fragility.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/views/ArtistView.vue

@@ -18,6 +18,7 @@
       :image-count="store.imageCount"
       :post-count="store.postCount"
       :last-added="store.lastAdded"
+      @rename="onRename"
     />
     <v-container fluid class="pt-2 pb-4">
       <!-- "N new since last visit" banner. Visible only on the initial
@@ -59,6 +60,7 @@ import { computed, ref, watch } from 'vue'
 import { useRoute } from 'vue-router'
 
 import { useArtistStore } from '../stores/artist.js'
+import { toast } from '../utils/toast.js'
 import ArtistHeader from '../components/artist/ArtistHeader.vue'
 import ArtistPostsTab from '../components/artist/ArtistPostsTab.vue'
 import ArtistGalleryTab from '../components/artist/ArtistGalleryTab.vue'
@@ -76,6 +78,17 @@ const { tab, resolve } = useTabQuery(
   () => ((store.postCount ?? 0) > 0 ? 'posts' : 'gallery'),
 )
 
+// Rename the artist's display name (#130). Slug/route unchanged, so no
+// navigation — the header just reflects the new name; also refresh the tab title.
+async function onRename (name) {
+  try {
+    await store.rename(name)
+    document.title = `${store.overview.name} — FabledCurator`
+  } catch (e) {
+    toast({ text: `Rename failed: ${e.message}`, type: 'error' })
+  }
+}
+
 // One-shot banner — reset on each new artist-slug load so it re-appears
 // when navigating between artists that each have unseen content.
 const unseenBanner = ref(false)