feat: add feature flag to disable Essentials tab in node library (#9067)

## Summary

Add a `node_library_essentials_enabled` feature flag to gate the
Essentials tab, allowing the rest of the new node library to ship while
the Essentials tab is finalized.

## Changes

- **What**: New feature flag (`node_library_essentials_enabled`) that
hides the Essentials tab in the node library sidebar and search category
sidebar. Defaults to `true` in dev/nightly builds, `false` in
production. Overridable via remote config or server feature flags. Falls
back to the "All" tab if a user previously had Essentials selected.

**Disabled UI**

<img width="547" height="782" alt="image"
src="https://github.com/user-attachments/assets/bcfcecd4-cbae-4d7b-9bcc-64bdf57929e2"
/>

**Enabled UI**

<img width="547" height="782" alt="image"
src="https://github.com/user-attachments/assets/0fb030ea-3bde-475e-982b-45e8f190cb8f"
/>


## Review Focus

- Feature flag pattern follows existing conventions (e.g.
`linearToggleEnabled`)
- Fallback behavior when essentials tab was previously selected by user

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9067-feat-add-feature-flag-to-disable-Essentials-tab-in-node-library-30e6d73d36508103b3cad9fc5d260611)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

src/components/sidebar/tabs/NodeLibrarySidebarTabV2.vue

@@ -52,7 +52,7 @@
             :value="tab.value"
             :class="
               cn(
-                'select-none border-none outline-none px-3 py-2 rounded-lg cursor-pointer',
+                'flex-1 text-center select-none border-none outline-none px-3 py-2 rounded-lg cursor-pointer',
                 'text-sm text-foreground transition-colors',
                 selectedTab === tab.value
                   ? 'bg-comfy-input font-bold'
@@ -70,7 +70,9 @@
       <!-- Tab content (scrollable) -->
       <TabsRoot v-model="selectedTab" class="h-full">
         <EssentialNodesPanel
-          v-if="selectedTab === 'essentials'"
+          v-if="
+            flags.nodeLibraryEssentialsEnabled && selectedTab === 'essentials'
+          "
           v-model:expanded-keys="expandedKeys"
           :root="renderedEssentialRoot"
           @node-click="handleNodeClick"
@@ -109,10 +111,11 @@ import {
   TabsRoot,
   TabsTrigger
 } from 'reka-ui'
-import { computed, nextTick, onMounted, ref } from 'vue'
+import { computed, nextTick, onMounted, ref, watchEffect } from 'vue'
 import { useI18n } from 'vue-i18n'
 
 import SearchBox from '@/components/common/SearchBoxV2.vue'
+import { useFeatureFlags } from '@/composables/useFeatureFlags'
 import { useNodeDragToCanvas } from '@/composables/node/useNodeDragToCanvas'
 import { usePerTabState } from '@/composables/usePerTabState'
 import {
@@ -136,11 +139,22 @@ import EssentialNodesPanel from './nodeLibrary/EssentialNodesPanel.vue'
 import NodeDragPreview from './nodeLibrary/NodeDragPreview.vue'
 import SidebarTabTemplate from './SidebarTabTemplate.vue'
 
+const { flags } = useFeatureFlags()
+
 const selectedTab = useLocalStorage<TabId>(
   'Comfy.NodeLibrary.Tab',
   DEFAULT_TAB_ID
 )
 
+watchEffect(() => {
+  if (
+    !flags.nodeLibraryEssentialsEnabled &&
+    selectedTab.value === 'essentials'
+  ) {
+    selectedTab.value = DEFAULT_TAB_ID
+  }
+})
+
 const sortOrderByTab = useLocalStorage<Record<TabId, SortingStrategyId>>(
   'Comfy.NodeLibrary.SortByTab',
   {
@@ -324,11 +338,21 @@ async function handleSearch() {
   expandedKeys.value = allKeys
 }
 
-const tabs = computed(() => [
-  { value: 'essentials', label: t('sideToolbar.nodeLibraryTab.essentials') },
-  { value: 'all', label: t('sideToolbar.nodeLibraryTab.allNodes') },
-  { value: 'custom', label: t('sideToolbar.nodeLibraryTab.custom') }
-])
+const tabs = computed(() => {
+  const baseTabs: Array<{ value: TabId; label: string }> = [
+    { value: 'all', label: t('sideToolbar.nodeLibraryTab.allNodes') },
+    { value: 'custom', label: t('sideToolbar.nodeLibraryTab.custom') }
+  ]
+  return flags.nodeLibraryEssentialsEnabled
+    ? [
+        {
+          value: 'essentials' as TabId,
+          label: t('sideToolbar.nodeLibraryTab.essentials')
+        },
+        ...baseTabs
+      ]
+    : baseTabs
+})
 
 onMounted(() => {
   searchBoxRef.value?.focus()