feat: unify sidebar panel header layout with SidebarTopArea component (#9740)

## Summary

Unify the search bar + action buttons layout across all left sidebar
panels (Node Library, Workflows, Model Library, Media Assets) using a
shared `SidebarTopArea` presentation component.

## Changes

- **What**:
- Add `SidebarTopArea.vue` — layout component with `flex-1` default slot
(search) and `#actions` slot (buttons), plus optional `bottomDivider`
prop
- Replace raw `<button>` elements in Node Library with `<Button
variant="secondary" size="icon">`
- Replace reka-ui `TabsTrigger` with shared `Tab/TabList` component in
Node Library
- Move Media Assets tab list from hover-only `#tool-buttons` to
always-visible header below search area
- Unify spacing (`gap-2`, `p-2 2xl:px-4`) and divider styles across all
sidebar panels
- Remove unused `assetType` prop and header from
`AssetsSidebarGridView`/`AssetsSidebarListView`

## Review Focus

- `SidebarTopArea` API simplicity — just slots + one optional prop
- Node Library still requires `TabsRoot` in the body for reka-ui
`TabsContent` in child panels
- Media Assets tabs are now always visible instead of hover-only

[screen-capture
(1).webm](https://github.com/user-attachments/assets/fe1d8f7b-5674-4bb3-9842-569e4c3af6c9)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9740-feat-unify-sidebar-panel-header-layout-with-SidebarTopArea-component-3206d73d365081ea8ba7fd6ac54e0169)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>

src/components/sidebar/tabs/nodeLibrary/AllNodesPanel.vue

@@ -1,5 +1,5 @@
 <template>
-  <TabsContent value="all" class="h-full flex-1 overflow-y-auto">
+  <div class="h-full flex-1 overflow-y-auto">
     <!-- Favorites section -->
     <h3
       class="mb-0 px-4 py-2 text-xs font-medium tracking-wide text-muted-foreground uppercase"
@@ -34,11 +34,10 @@
         @add-to-favorites="handleAddToFavorites"
       />
     </div>
-  </TabsContent>
+  </div>
 </template>
 
 <script setup lang="ts">
-import { TabsContent } from 'reka-ui'
 import { computed } from 'vue'
 
 import TreeExplorerV2 from '@/components/common/TreeExplorerV2.vue'