feat(node): show Enter Subgraph and Error buttons side by side in node footer (#9126)

## Summary
Show the \"Enter Subgraph\" and \"Error\" buttons simultaneously in the
node footer when a subgraph node has errors, instead of only showing the
Error button.

## Changes
- **What**: Replaced the single mutually-exclusive `Button` in the node
footer with a flex container that can display both the \"Enter
Subgraph\" button and the \"Error\" button side by side, separated by a
divider
- **What**: When a subgraph node has errors, the Enter button shows a
short label \"Enter\" to fit alongside the Error button; otherwise it
shows the full \"Enter Subgraph\" label
- **What**: Advanced inputs toggle button is now explicitly restricted
to non-subgraph nodes (preserving existing behavior)
- **What**: Added `"enter": "Enter"` i18n key for the shortened subgraph
entry label

## Review Focus
- Layout behavior when both buttons are visible (subgraph node with
errors)
- Collapsed vs. expanded node states with the new flex container
- The `divide-x divide-component-node-border` divider between buttons

> Note: May need to backport to a stable release branch.

## Screenshot


https://github.com/user-attachments/assets/1eb4afe0-bf82-4677-ad86-6e15a9c0a487



- Fixes <!-- #ISSUE_NUMBER -->

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9126-feat-node-show-Enter-Subgraph-and-Error-buttons-side-by-side-in-node-footer-3106d73d3650818a9afdeb51813825d9)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -69,6 +69,7 @@
     "icon": "Icon",
     "color": "Color",
     "error": "Error",
+    "enter": "Enter",
     "enterSubgraph": "Enter Subgraph",
     "resizeFromBottomRight": "Resize from bottom-right corner",
     "resizeFromTopRight": "Resize from top-right corner",