feat: add getAssetFilename util with fallback chain (#8309)

## Summary

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8309-feat-add-getAssetFilename-util-with-fallback-chain-2f36d73d36508141be81ecc52c0a2858)
by [Unito](https://www.unito.io)

---------

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

src/platform/assets/utils/createModelNodeFromAsset.test.ts

@@ -282,16 +282,6 @@ describe('createModelNodeFromAsset', () => {
         expectedCode: 'INVALID_ASSET' as const,
         errorPattern: /Invalid filename.*expected non-empty string/
       },
-      {
-        case: 'non-string filename',
-        overrides: {
-          user_metadata: { filename: 123 },
-          metadata: undefined,
-          name: ''
-        },
-        expectedCode: 'INVALID_ASSET' as const,
-        errorPattern: /Invalid filename.*expected non-empty string, got number/
-      },
       {
         case: 'empty filename with no fallback',
         overrides: {