test(assets-sidebar): add comprehensive E2E tests for Assets browser panel (#10616)

## Summary
- Extend `AssetsSidebarTab` page object with selectors for search, view
mode, asset cards, selection footer, context menu, and folder view
navigation
- Add mock data factories (`createMockJob`, `createMockJobs`,
`createMockImportedFiles`) to `AssetsHelper` for generating realistic
test fixtures
- Write 30 E2E test cases across 10 categories covering the Assets
browser sidebar panel

## Test coverage added

| Category | Tests | Details |
|----------|-------|---------|
| Empty states | 3 | Generated/Imported empty copy, zero cards |
| Tab navigation | 3 | Default tab, switching, search reset on tab
change |
| Grid view display | 2 | Generated card rendering, Imported tab assets
|
| View mode toggle | 2 | Grid↔List switching via settings menu |
| Search | 4 | Input visibility, filtering, clearing, no-match state |
| Selection | 5 | Click select, Ctrl+click multi, footer, deselect all,
tab-switch clear |
| Context menu | 7 | Right-click menu,
Download/Inspect/Delete/CopyJobID/Workflow actions, bulk menu |
| Bulk actions | 3 | Download/Delete buttons, selection count display |
| Pagination | 1 | Large job set initial load |
| Settings menu | 1 | View mode options visibility |

## Context
Part of [FixIt
Burndown](https://www.notion.so/comfy-org/FixIt-Burndown-32e6d73d365080609a81cdc9bc884460)
— "Untested Side Panels: Assets browser" assigned to @dante01yoon.

## Test plan
- [ ] Run `npx playwright test
browser_tests/tests/sidebar/assets.spec.ts` against local ComfyUI
backend
- [ ] Verify all 30 tests pass
- [ ] CI green

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10616-test-assets-sidebar-add-comprehensive-E2E-tests-for-Assets-browser-panel-3306d73d365081eeb237e559f56689bf)
by [Unito](https://www.unito.io)

src/components/sidebar/tabs/AssetsSidebarTab.vue

@@ -143,11 +143,16 @@
             <Button
               v-if="shouldShowDeleteButton"
               size="icon"
+              data-testid="assets-delete-selected"
               @click="handleDeleteSelected"
             >
               <i class="icon-[lucide--trash-2] size-4" />
             </Button>
-            <Button size="icon" @click="handleDownloadSelected">
+            <Button
+              size="icon"
+              data-testid="assets-download-selected"
+              @click="handleDownloadSelected"
+            >
               <i class="icon-[lucide--download] size-4" />
             </Button>
           </template>
@@ -156,12 +161,17 @@
             <Button
               v-if="shouldShowDeleteButton"
               variant="secondary"
+              data-testid="assets-delete-selected"
               @click="handleDeleteSelected"
             >
               <span>{{ $t('mediaAsset.selection.deleteSelected') }}</span>
               <i class="icon-[lucide--trash-2] size-4" />
             </Button>
-            <Button variant="secondary" @click="handleDownloadSelected">
+            <Button
+              variant="secondary"
+              data-testid="assets-download-selected"
+              @click="handleDownloadSelected"
+            >
               <span>{{ $t('mediaAsset.selection.downloadSelected') }}</span>
               <i class="icon-[lucide--download] size-4" />
             </Button>