feat(admin): add "Regenerate All GLB + USD" button

New endpoint POST /admin/settings/regenerate-all-canonical-scenes
queues GLB + USD master export for ALL completed CAD files, replacing
existing assets. Used after pipeline changes that affect tessellation
or normals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/Admin.tsx

@@ -237,6 +237,12 @@ export default function AdminPage() {
     onError: (e: any) => toast.error(e.response?.data?.detail || 'Failed'),
   })
 
+  const regenerateAllCanonicalScenesMut = useMutation({
+    mutationFn: () => api.post('/admin/settings/regenerate-all-canonical-scenes'),
+    onSuccess: (res) => toast.success(res.data.message || 'All canonical scenes re-queued'),
+    onError: (e: any) => toast.error(e.response?.data?.detail || 'Failed'),
+  })
+
   const [smtpDraft, setSmtpDraft] = useState<Partial<Settings>>({})
   const smtp = { ...settings, ...smtpDraft } as Settings
 
@@ -958,6 +964,18 @@ export default function AdminPage() {
                 </button>
                 <p className="text-xs text-content-muted">Queues geometry GLB + USD master for all completed CAD files missing a canonical scene.</p>
               </div>
+              <div className="flex flex-col gap-1">
+                <button
+                  onClick={() => regenerateAllCanonicalScenesMut.mutate()}
+                  disabled={regenerateAllCanonicalScenesMut.isPending}
+                  className="btn-secondary text-sm w-full justify-start"
+                  title="Re-export geometry GLB + USD master for ALL completed CAD files (overwrites existing)"
+                >
+                  <RefreshCw size={14} className={regenerateAllCanonicalScenesMut.isPending ? 'animate-spin' : ''} />
+                  {regenerateAllCanonicalScenesMut.isPending ? 'Queueing…' : 'Regenerate All GLB + USD'}
+                </button>
+                <p className="text-xs text-content-muted">Re-exports GLB and USD for all completed CAD files, replacing existing assets.</p>
+              </div>
               <div className="flex flex-col gap-1">
                 <button
                   onClick={() => importMediaAssetsMut.mutate()}