[fix] Correct Install All button visibility for manager UI states

- Install All Missing Custom Nodes button only shows for NEW_UI state
- Legacy UI state only shows Open Manager button
- Disabled state shows no buttons
- Matches original PR #5063 behavior exactly

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/components/dialog/content/LoadWorkflowWarning.vue

@@ -33,6 +33,7 @@
   </ListBox>
   <div v-if="showManagerButtons" class="flex justify-end py-3">
     <PackInstallButton
+      v-if="showInstallAllButton"
       :disabled="
         isLoading || !!error || missingNodePacks.length === 0 || isInstalling
       "
@@ -115,6 +116,11 @@ const showManagerButtons = computed(() => {
   return managerStateStore.managerUIState !== ManagerUIState.DISABLED
 })
 
+// Only show Install All button for NEW_UI (new manager with v4 support)
+const showInstallAllButton = computed(() => {
+  return managerStateStore.managerUIState === ManagerUIState.NEW_UI
+})
+
 const openManager = async () => {
   const state = managerStateStore.managerUIState