fix: make graph canvas toolbar visible on mobile (#10168)

## Summary

Fix the bottom-right graph canvas toolbar (zoom controls, fit-to-view,
minimap toggle) not being visible on mobile devices in normal graph
mode.

## Problem

PrimeVue applies `overflow: hidden` to all `.p-splitterpanel` elements
by default. The `GraphCanvasMenu` component is absolutely positioned
(`right-0 bottom-0`) inside the `graph-canvas-panel` SplitterPanel. On
mobile viewports, the panel's bounding box can be smaller than the full
canvas area, causing the toolbar to be clipped by the `overflow:
hidden`.

## Solution

Add `overflow-visible` to the `graph-canvas-panel` SplitterPanel class
to override PrimeVue's default `overflow: hidden`. This allows the
absolutely-positioned toolbar (and minimap) to remain visible regardless
of viewport size.

<img width="873" height="1056" alt="image"
src="https://github.com/user-attachments/assets/7239a5ce-8ce8-4e1d-a8ff-6d6d3c61f5da"
/>


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10168-fix-make-graph-canvas-toolbar-visible-on-mobile-3266d73d36508130b675e839cb748fd5)
by [Unito](https://www.unito.io)

src/components/LiteGraphCanvasSplitterOverlay.vue

@@ -72,7 +72,7 @@
             state-storage="local"
             @resizestart="onResizestart"
           >
-            <SplitterPanel class="graph-canvas-panel relative">
+            <SplitterPanel class="graph-canvas-panel relative overflow-visible">
               <slot name="graph-canvas-panel" />
             </SplitterPanel>
             <SplitterPanel