[feat] Add ownership filter to model browser (#7201)

## Summary
Adds a dropdown filter to the model browser that allows users to filter
assets by ownership (All, My models, Public models), based on the
`is_immutable` property.

## Changes
- **Filter UI**: Added ownership dropdown in
[AssetFilterBar.vue](src/platform/assets/components/AssetFilterBar.vue#L30-L38)
that only appears when user has uploaded models
- **Filter Logic**: Implemented `filterByOwnership` function in
[useAssetBrowser.ts](src/platform/assets/composables/useAssetBrowser.ts#L38-L45)
to filter by `is_immutable` property
- **i18n**: Added translation strings for ownership filter options
- **Tests**: Added comprehensive tests for ownership filtering in both
composable and component test files

## Review Focus
- The ownership filter visibility logic correctly checks for mutable
assets (`!is_immutable`)
- Default filter value is 'all' to show all models initially
- Filter integrates cleanly with existing file format and base model
filters

🤖 Generated with [Claude Code](https://claude.com/claude-code)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7201-feat-Add-ownership-filter-to-model-browser-2c16d73d365081f280f6d1e42e5400af)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/platform/assets/fixtures/ui-mock-assets.ts

@@ -146,9 +146,15 @@ export function createAssetWithoutUserMetadata() {
   return asset
 }
 
-export function createAssetWithSpecificExtension(extension: string) {
+export function createAssetWithSpecificExtension(
+  extension: string,
+  isImmutable?: boolean
+) {
   const asset = createMockAssets(1)[0]
   asset.name = `test-model.${extension}`
+  if (isImmutable !== undefined) {
+    asset.is_immutable = isImmutable
+  }
   return asset
 }