perf(AssetBrowserModal): virtualize asset grid to reduce network requests (#7919)

## Problem

The `AssetBrowserModal` triggers hundreds of network requests when
opened because `AssetGrid.vue` renders all asset cards immediately using
a simple `v-for` loop. Each `AssetCard` loads its thumbnail image,
causing a flood of simultaneous requests.

## Solution

Replace the simple `v-for` with the existing `VirtualGrid` component
(already used in `AssetsSidebarTab.vue` and `ManagerDialogContent.vue`)
to only render visible items plus a small buffer.

## Changes

- **`AssetGrid.vue`**: Use `VirtualGrid` with computed `assetsWithKey`
that adds the required `key` property from `asset.id`
- **`BaseModalLayout.vue`**: Add `flex-1` to content container for
proper height calculation (required for `VirtualGrid` to work)

## Testing

- All 130 asset-related tests pass
- TypeScript and lint checks pass

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7919-perf-AssetBrowserModal-virtualize-asset-grid-to-reduce-network-requests-2e36d73d365081a1be18d0eb33b7ef8a)
by [Unito](https://www.unito.io)

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

src/components/widget/layout/BaseModalLayout.vue

@@ -82,7 +82,7 @@
               {{ contentTitle }}
             </h2>
             <div
-              class="min-h-0 px-6 pt-0 pb-10 overflow-y-auto scrollbar-custom"
+              class="min-h-0 flex-1 px-6 pt-0 pb-10 overflow-y-auto scrollbar-custom"
             >
               <slot name="content"></slot>
             </div>

src/platform/assets/components/AssetGrid.vue

@@ -1,28 +1,21 @@
 <template>
   <div
     data-component-id="AssetGrid"
-    :class="
-      cn('grid grid-cols-[repeat(auto-fill,minmax(15rem,1fr))] gap-4 p-2')
-    "
+    class="h-full"
     role="grid"
     :aria-label="$t('assetBrowser.assetCollection')"
     :aria-rowcount="-1"
     :aria-colcount="-1"
     :aria-setsize="assets.length"
   >
-    <!-- Loading state -->
-    <div
-      v-if="loading"
-      class="col-span-full flex items-center justify-center py-20"
-    >
+    <div v-if="loading" class="flex h-full items-center justify-center py-20">
       <i
         class="icon-[lucide--loader] size-12 animate-spin text-muted-foreground"
       />
     </div>
-    <!-- Empty state -->
     <div
       v-else-if="assets.length === 0"
-      class="col-span-full flex flex-col items-center justify-center py-16 text-muted-foreground"
+      class="flex h-full flex-col items-center justify-center py-16 text-muted-foreground"
     >
       <i class="mb-4 icon-[lucide--search] size-10" />
       <h3 class="mb-2 text-lg font-medium">
@@ -30,24 +23,33 @@
       </h3>
       <p class="text-sm">{{ $t('assetBrowser.tryAdjustingFilters') }}</p>
     </div>
-    <template v-else>
-      <AssetCard
-        v-for="asset in assets"
-        :key="asset.id"
-        :asset="asset"
-        :interactive="true"
-        @select="$emit('assetSelect', $event)"
-      />
-    </template>
+    <VirtualGrid
+      v-else
+      :items="assetsWithKey"
+      :grid-style="gridStyle"
+      :default-item-height="320"
+      :default-item-width="240"
+    >
+      <template #item="{ item }">
+        <AssetCard
+          :asset="item"
+          :interactive="true"
+          @select="$emit('assetSelect', $event)"
+        />
+      </template>
+    </VirtualGrid>
   </div>
 </template>
 
 <script setup lang="ts">
+import type { CSSProperties } from 'vue'
+import { computed } from 'vue'
+
+import VirtualGrid from '@/components/common/VirtualGrid.vue'
 import AssetCard from '@/platform/assets/components/AssetCard.vue'
 import type { AssetDisplayItem } from '@/platform/assets/composables/useAssetBrowser'
-import { cn } from '@/utils/tailwindUtil'
 
-defineProps<{
+const { assets } = defineProps<{
   assets: AssetDisplayItem[]
   loading?: boolean
 }>()
@@ -55,4 +57,15 @@ defineProps<{
 defineEmits<{
   assetSelect: [asset: AssetDisplayItem]
 }>()
+
+const assetsWithKey = computed(() =>
+  assets.map((asset) => ({ ...asset, key: asset.id }))
+)
+
+const gridStyle: Partial<CSSProperties> = {
+  display: 'grid',
+  gridTemplateColumns: 'repeat(auto-fill, minmax(15rem, 1fr))',
+  gap: '1rem',
+  padding: '0.5rem'
+}
 </script>