Allow artworks to have one primary category and extra secondaries.

Keep artwork_category as membership, store a deterministic primary_category_id, and let upload plus studio pick up to five additional same-type categories without changing canonical URLs.

resources/js/lib/uploadUtils.js

@@ -103,6 +103,33 @@ export function buildCategoryTree(contentTypes = []) {
   return Array.from(rootsById.values())
 }
 
+export function compareCategoryNames(a, b) {
+  return String(a?.name || '').localeCompare(String(b?.name || ''), undefined, {
+    numeric: true,
+    sensitivity: 'base',
+  })
+}
+
+export function additionalCategoryOptions(roots = [], primaryId = '') {
+  const options = []
+  const seen = new Set()
+  const primary = String(primaryId || '')
+
+  roots.forEach((root) => {
+    const items = [root, ...(Array.isArray(root.children) ? root.children : [])]
+    items.forEach((item) => {
+      const id = String(item?.id || '')
+      if (!id || id === primary || seen.has(id)) {
+        return
+      }
+      seen.add(id)
+      options.push({ id, name: item.name || `Category ${id}` })
+    })
+  })
+
+  return options.sort(compareCategoryNames)
+}
+
 // ─── Content type helpers ─────────────────────────────────────────────────────
 export function getContentTypeValue(type) {
   if (!type) return ''