[style] Update error/subgraph node footer design with layered overlay approach (#9360)

## Summary

Refactors the error and subgraph node footer UI by extracting a
dedicated `NodeFooter` component and replacing the CSS `outline`
approach with a layered border overlay for selection/executing state
indicators.

## Changes

- **What**: Extracted `NodeFooter.vue` from `LGraphNode.vue` to
encapsulate the footer tab logic (subgraph enter, error, advanced
inputs). Replaced CSS `outline` with an absolutely-positioned border
overlay div for selection and executing state. Added a separate root
border overlay div for the node body border. Removed unused
`isTransparent` function from `colorUtil.ts`.
- **Dependencies**: None

## Review Focus

- The layered overlay approach (`absolute -inset-[3px] border-3`) for
selection/executing outlines vs the previous `outline-3` approach —
ensures the outline renders outside the node bounds correctly including
the footer area
- `NodeFooter` handles 4 cases: subgraph+error (dual tabs), error only,
subgraph only, advanced inputs — verify edge cases render correctly
- Resize handle bottom offset adjustments for nodes with footers
(`hasFooter`)

## Screenshots
<img width="1142" height="603" alt="image"
src="https://github.com/user-attachments/assets/e0d401f0-8516-4f5f-ab77-48a79530f4bd"
/>
<img width="1175" height="577" alt="image"
src="https://github.com/user-attachments/assets/bcf08fff-728a-491c-add9-5b96d2f3bfce"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9360-style-Update-error-subgraph-node-footer-design-with-layered-overlay-approach-3186d73d365081b2ac31f166f4d1944a)
by [Unito](https://www.unito.io)

---------

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

browser_tests/fixtures/VueNodeHelpers.ts

@@ -172,6 +172,19 @@ export class VueNodeHelpers {
   async enterSubgraph(nodeId?: string): Promise<void> {
     const locator = nodeId ? this.getNodeLocator(nodeId) : this.page
     const editButton = locator.getByTestId(TestIds.widgets.subgraphEnterButton)
-    await editButton.click()
+
+    // The footer tab button extends below the node body (visible area),
+    // but its bounding box center overlaps the node body div.
+    // Click at the bottom 25% of the button which is the genuinely visible
+    // and unobstructed area outside the node body boundary.
+    const box = await editButton.boundingBox()
+    if (!box) {
+      throw new Error(
+        'subgraph-enter-button has no bounding box: element may be hidden or not in DOM'
+      )
+    }
+    await editButton.click({
+      position: { x: box.width / 2, y: box.height * 0.75 }
+    })
   }
 }