[Bug]: Side panel button row clips / can't scroll on narrow (≤768px, mobile) viewports

### Summary

On narrow (mobile / touch) viewports, the **right side panel's action-button row does not wrap and the nested splitter panel does not scroll vertically**, so buttons overflow horizontally and become **clipped and unreachable**. A rigid-width inner column compounds it. On a phone this makes part of the side panel simply unusable — there is no touch-reachable way to get to the overflowed controls.

### Steps to reproduce

1. Open ComfyUI in a viewport ≤ 768px wide (a phone, or DevTools device toolbar).
2. Open the right side panel (the toolbox / properties splitter panel).
3. Observe the button row: it overflows its container rather than wrapping, the panel does not scroll vertically to reveal the overflow, and a fixed-width column pushes content off-screen.

### Expected

On narrow viewports the side-panel controls should either wrap onto multiple rows or the panel should scroll, so **every control stays reachable on a touch device**.

### Actual

The button row stays single-line with rigid widths, the nested splitter panel has no vertical scroll, and overflowed buttons are clipped and cannot be reached.

### Environment

- `comfyui-frontend-package` **1.45.20** (also reproduced on the surrounding recent releases)
- Touch / narrow viewport (≤ 768px); observed via live DevTools analysis, 2026-07

### Affected area (observed, caveated)

The PrimeVue splitter (`.p-splitterpanel`, `.p-splitterpanel-nested`) that hosts the side panel. The specific class chains below are **compiled Tailwind utilities** and are expected to be volatile between releases — they're included only to point at the region, not as a stable contract:

- the button row: `.p-splitterpanel .flex.gap-x-0.5`
- the fixed-width column: `.p-splitterpanel .mx-1.flex.flex-col.items-end.gap-1`

### Workaround (scoped CSS)

A narrow-viewport-scoped override restores usability without touching desktop:

```css
@media (max-width: 768px) {
.p-splitterpanel .flex.gap-x-0\.5 { flex-wrap: wrap; }
.p-splitterpanel.p-splitterpanel-nested { overflow-y: auto; }
.p-splitterpanel .mx-1.flex.flex-col.items-end.gap-1 {
width: auto; max-width: 100%; flex-shrink: 1;
}
}
```

This is currently shipped as a stopgap in a community custom-node pack ([`comfyui-touch-shim`](https://github.com/laurigates/comfyui-touch-shim), a home for small mobile/touch fixes for upstream frontend bugs) and will be removed the release this is fixed upstream. Happy to open a PR against the real components if that's welcome — the proper fix likely belongs in the splitter/toolbox layout rather than a media-query patch on compiled classes.

### Related

- #13068 — DOM widget width halved when the right side panel is open
- #7164 — Option to display toolbox buttons in the right side panel

Start by locating the PrimeVue splitter and toolbox layout components described in the issue, then reproduce the problem at a viewport of 768px or narrower. Verify that the action controls wrap or become vertically reachable on touch-sized screens, while desktop behavior remains unchanged.

Written by the indexing model from the issue text.