chore: migrate tests from tests-ui/ to colocate with source files (#7811)

## Summary

Migrates all unit tests from `tests-ui/` to colocate with their source
files in `src/`, improving discoverability and maintainability.

## Changes

- **What**: Relocated all unit tests to be adjacent to the code they
test, following the `<source>.test.ts` naming convention
- **Config**: Updated `vitest.config.ts` to remove `tests-ui` include
pattern and `@tests-ui` alias
- **Docs**: Moved testing documentation to `docs/testing/` with updated
paths and patterns

## Review Focus

- Migration patterns documented in
`temp/plans/migrate-tests-ui-to-src.md`
- Tests use `@/` path aliases instead of relative imports
- Shared fixtures placed in `__fixtures__/` directories

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7811-chore-migrate-tests-from-tests-ui-to-colocate-with-source-files-2da6d73d36508147a4cce85365dee614)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

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

@@ -0,0 +1,65 @@
+import { describe, expect, it } from 'vitest'
+
+import type { AssetItem } from '@/platform/assets/schemas/assetSchema'
+import {
+  getAssetBaseModel,
+  getAssetDescription
+} from '@/platform/assets/utils/assetMetadataUtils'
+
+describe('assetMetadataUtils', () => {
+  const mockAsset: AssetItem = {
+    id: 'test-id',
+    name: 'test-model',
+    asset_hash: 'hash123',
+    size: 1024,
+    mime_type: 'application/octet-stream',
+    tags: ['models', 'checkpoints'],
+    created_at: '2024-01-01T00:00:00Z',
+    updated_at: '2024-01-01T00:00:00Z',
+    last_access_time: '2024-01-01T00:00:00Z'
+  }
+
+  describe('getAssetDescription', () => {
+    it('should return string description when present', () => {
+      const asset = {
+        ...mockAsset,
+        user_metadata: { description: 'A test model' }
+      }
+      expect(getAssetDescription(asset)).toBe('A test model')
+    })
+
+    it('should return null when description is not a string', () => {
+      const asset = {
+        ...mockAsset,
+        user_metadata: { description: 123 }
+      }
+      expect(getAssetDescription(asset)).toBeNull()
+    })
+
+    it('should return null when no metadata', () => {
+      expect(getAssetDescription(mockAsset)).toBeNull()
+    })
+  })
+
+  describe('getAssetBaseModel', () => {
+    it('should return string base_model when present', () => {
+      const asset = {
+        ...mockAsset,
+        user_metadata: { base_model: 'SDXL' }
+      }
+      expect(getAssetBaseModel(asset)).toBe('SDXL')
+    })
+
+    it('should return null when base_model is not a string', () => {
+      const asset = {
+        ...mockAsset,
+        user_metadata: { base_model: 123 }
+      }
+      expect(getAssetBaseModel(asset)).toBeNull()
+    })
+
+    it('should return null when no metadata', () => {
+      expect(getAssetBaseModel(mockAsset)).toBeNull()
+    })
+  })
+})