feat: add manager enable hint for OSS local users (#9377)

## Summary

When ComfyUI Manager is disabled, OSS local users see a hint in the
Missing Nodes panel explaining how to install and enable it.

## Changes

- **What**: Added an inline hint in `MissingNodeCard` that renders when
the user is on OSS (non-Cloud) and Manager is not active
(`showInfoButton` is false). The hint shows the pip install command and
the `--enable-manager` startup flag, formatted as inline `<code>`
snippets via `i18n-t` interpolation.

## Review Focus

- The `showManagerHint` computed is intentionally simple: `!isCloud &&
!props.showInfoButton`. `showInfoButton` is the existing signal for
whether Manager is available/enabled.
- Styling uses existing semantic tokens (`bg-comfy-menu-bg`,
`text-comfy-input-foreground`) to match the rest of the panel.

## Screenshot
<img width="642" height="452" alt="image"
src="https://github.com/user-attachments/assets/d08280d3-b4a0-4613-b092-1baa49f0b091"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9377-feat-add-manager-enable-hint-for-OSS-local-users-3196d73d365081a19037c8f55f11d1eb)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -3207,6 +3207,7 @@
       "unsupportedTitle": "Unsupported Node Packs",
       "cloudMessage": "This workflow requires custom nodes not yet available on Comfy Cloud.",
       "ossMessage": "This workflow uses custom nodes you haven't installed yet.",
+      "ossManagerDisabledHint": "To install missing nodes, first run {pipCmd} in your Python environment to install Node Manager, then restart ComfyUI with the {flag} flag.",
       "installAll": "Install All",
       "installNodePack": "Install node pack",
       "unknownPack": "Unknown pack",