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)

browser_tests/tests/mobileBaseline.spec.ts

@@ -24,6 +24,20 @@ test.describe(
       )
     })
 
+    test('@mobile graph canvas toolbar visible', async ({ comfyPage }) => {
+      await comfyPage.settings.setSetting('Comfy.Graph.CanvasMenu', true)
+      await comfyPage.nextFrame()
+
+      const minimapButton = comfyPage.page.getByTestId(
+        TestIds.canvas.toggleMinimapButton
+      )
+      await expect(minimapButton).toBeVisible()
+
+      await expect(comfyPage.canvas).toHaveScreenshot(
+        'mobile-graph-canvas-toolbar.png'
+      )
+    })
+
     test('@mobile settings dialog', async ({ comfyPage }) => {
       await comfyPage.settingDialog.open()
       await comfyPage.nextFrame()