feat(server-config): add legacy manager UI toggle (#7478)

Adds a Desktop (Electron) Server-Config setting for
`--enable-manager-legacy-ui` so users can opt into ComfyUI-Manager’s
legacy UI.

- Adds `enable-manager-legacy-ui` to `SERVER_CONFIG_ITEMS`
- Adds EN i18n label + tooltip

Note: this PR only adds the setting/flag wiring; it does not change
restart behavior in Desktop.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7478-feat-server-config-add-legacy-manager-UI-toggle-2ca6d73d365081a79bb2c376506f5346)
by [Unito](https://www.unito.io)


> [!NOTE]
> This is a stacked PR. (main <=
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7478 <=
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7479)

src/constants/serverConfig.ts

@@ -389,6 +389,13 @@ export const SERVER_CONFIG_ITEMS: ServerConfig<any>[] = [
     type: 'boolean',
     defaultValue: false
   },
+  {
+    id: 'enable-manager-legacy-ui',
+    name: 'Use legacy Manager UI',
+    tooltip: 'Uses the legacy ComfyUI-Manager UI instead of the new UI.',
+    type: 'boolean',
+    defaultValue: false
+  },
   {
     id: 'disable-all-custom-nodes',
     name: 'Disable loading all custom nodes.',

src/locales/en/main.json

@@ -1333,6 +1333,10 @@
     "disable-metadata": {
       "name": "Disable saving prompt metadata in files."
     },
+    "enable-manager-legacy-ui": {
+      "name": "Use legacy Manager UI",
+      "tooltip": "Uses the legacy ComfyUI-Manager UI instead of the new UI."
+    },
     "disable-all-custom-nodes": {
       "name": "Disable loading all custom nodes."
     },
@@ -2444,4 +2448,4 @@
     "recentReleases": "Recent releases",
     "helpCenterMenu": "Help Center Menu"
   }
-}
+}