[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/locales/en/main.json

@@ -2160,15 +2160,19 @@
     "noModelsInFolder": "No {type} available in this folder",
     "notSureLeaveAsIs": "Not sure? Just leave this as is",
     "onlyCivitaiUrlsSupported": "Only Civitai URLs are supported",
+    "ownership": "Ownership",
+    "ownershipAll": "All",
+    "ownershipMyModels": "My models",
+    "ownershipPublicModels": "Public models",
     "selectFrameworks": "Select Frameworks",
     "selectModelType": "Select model type",
     "selectProjects": "Select Projects",
     "sortAZ": "A-Z",
     "sortBy": "Sort by",
-    "sortingType": "Sorting Type",
     "sortPopular": "Popular",
     "sortRecent": "Recent",
     "sortZA": "Z-A",
+    "sortingType": "Sorting Type",
     "tags": "Tags",
     "tagsHelp": "Separate tags with commas",
     "tagsPlaceholder": "e.g., models, checkpoint",