fix: Button sizing in modals and asset browser (#7920)

## Summary

Fix button sizing inconsistencies in modal dialogs and the asset
browser.

## Changes

- **What**: Fix Import button using responsive size (`lg`/`icon` based
on breakpoint) and ensure Modal Close button has explicit `w-10` width
for consistent sizing.

## Review Focus

Button sizing consistency across the modal UI.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7920-fix-Button-sizing-in-modals-and-asset-browser-2e36d73d365081fc997af8be1e928049)
by [Unito](https://www.unito.io)

src/platform/assets/components/AssetBrowserModal.vue

@@ -32,7 +32,7 @@
         <Button
           v-if="isUploadButtonEnabled"
           variant="primary"
-          :size="breakpoints.md ? 'md' : 'icon'"
+          :size="breakpoints.md ? 'lg' : 'icon'"
           data-attr="upload-model-button"
           @click="showUploadDialog"
         >