fix: use consistent chevron icon in Vue node dropdown widgets (#8576)

## Summary

Fixes styling inconsistency where Vue node select widget chevrons look
different between dropdown implementations.

## Changes

- **What**: Added `#dropdownicon` slot to `WidgetSelectDefault.vue`
using Lucide chevron icon with
`text-component-node-foreground-secondary` styling, matching
`FormDropdownInput.vue`

## Review Focus

Both dropdown implementations now use identical chevron icons with
consistent sizing (`size-4`) and color tokens.

Fixes #COM-11645


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Style**
* Updated select/dropdown appearance: replaced the previous icon
rendering with a customizable dropdown icon slot, improving visual
consistency and allowing a custom icon to display in select controls
across the UI. This change affects only presentation—no behavior or data
handling was altered.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8576-fix-use-consistent-chevron-icon-in-Vue-node-dropdown-widgets-2fc6d73d3650814e923bcbee83fae498)
by [Unito](https://www.unito.io)

---------

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

src/renderer/extensions/vueNodes/widgets/components/WidgetSelectDefault.vue

@@ -17,7 +17,13 @@
         overlay: 'w-fit min-w-full'
       }"
       data-capture-wheel="true"
-    />
+    >
+      <template #dropdownicon>
+        <i
+          class="icon-[lucide--chevron-down] size-4 text-component-node-foreground-secondary"
+        />
+      </template>
+    </SelectPlus>
     <div class="absolute top-5 right-8 h-4 w-7 -translate-y-4/5 flex">
       <slot />
     </div>