Cleanup: Sidebar Tabs component and style alignment (#7215)

## Summary

Unify the current sidebar tabs, structurally and aesthetically.

## Changes

- Removes the Assets only Layout
- Standardizes the title styling and spacing across the tabs.

## Review Focus

<!-- Critical design decisions or edge cases that need attention -->

<!-- If this PR fixes an issue, uncomment and update the line below -->
<!-- Fixes #ISSUE_NUMBER -->

## Screenshots (if applicable)

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┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7215-WIP-Sidebar-Tabs-component-and-style-alignment-2c26d73d3650817193bfd752e0d0bbde)
by [Unito](https://www.unito.io)

src/components/sidebar/tabs/NodeLibrarySidebarTab.vue

@@ -3,7 +3,6 @@
     <SidebarTabTemplate
       v-if="!isHelpOpen"
       :title="$t('sideToolbar.nodeLibrary')"
-      class="bg-(--p-tree-background)"
     >
       <template #tool-buttons>
         <Button