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)

browser_tests/fixtures/helpers/AssetsHelper.ts

@@ -5,6 +5,63 @@ import type { RawJobListItem } from '../../../src/platform/remote/comfyui/jobs/j
 const jobsListRoutePattern = /\/api\/jobs(?:\?.*)?$/
 const inputFilesRoutePattern = /\/internal\/files\/input(?:\?.*)?$/
 
+/** Factory to create a mock completed job with preview output. */
+export function createMockJob(
+  overrides: Partial<RawJobListItem> & { id: string }
+): RawJobListItem {
+  const now = Date.now() / 1000
+  return {
+    status: 'completed',
+    create_time: now,
+    execution_start_time: now,
+    execution_end_time: now + 5,
+    preview_output: {
+      filename: `output_${overrides.id}.png`,
+      subfolder: '',
+      type: 'output',
+      nodeId: '1',
+      mediaType: 'images'
+    },
+    outputs_count: 1,
+    priority: 0,
+    ...overrides
+  }
+}
+
+/** Create multiple mock jobs with sequential IDs and staggered timestamps. */
+export function createMockJobs(
+  count: number,
+  baseOverrides?: Partial<RawJobListItem>
+): RawJobListItem[] {
+  const now = Date.now() / 1000
+  return Array.from({ length: count }, (_, i) =>
+    createMockJob({
+      id: `job-${String(i + 1).padStart(3, '0')}`,
+      create_time: now - i * 60,
+      execution_start_time: now - i * 60,
+      execution_end_time: now - i * 60 + 5 + i,
+      preview_output: {
+        filename: `image_${String(i + 1).padStart(3, '0')}.png`,
+        subfolder: '',
+        type: 'output',
+        nodeId: '1',
+        mediaType: 'images'
+      },
+      ...baseOverrides
+    })
+  )
+}
+
+/** Create mock imported file names with various media types. */
+export function createMockImportedFiles(count: number): string[] {
+  const extensions = ['png', 'jpg', 'mp4', 'wav', 'glb', 'txt']
+  return Array.from(
+    { length: count },
+    (_, i) =>
+      `imported_${String(i + 1).padStart(3, '0')}.${extensions[i % extensions.length]}`
+  )
+}
+
 function parseLimit(url: URL, total: number): number {
   const value = Number(url.searchParams.get('limit'))
   if (!Number.isInteger(value) || value <= 0) {