test(e2e): add download flow tests and fix status CSS classes

- Add Playwright E2E tests covering real user download journeys:
  - Search anime → choose episodes → trigger download (with toast)
  - Real file download via static fixture and verify completion in UI
  - Click new release on homepage → switch to anime search tab
  - Search for series and display mocked results
- Fix bug in downloads_list.html: CSS classes used task.status (enum)
  which rendered as 'status-DownloadStatus.COMPLETED' instead of
  'status-completed'. Use task.status.value for correct CSS class names.
- Add static test fixture (20KB fake MP4) for reliable download tests
- All 16 E2E tests passing (12 existing + 4 new)

templates/components/downloads_list.html

@@ -1,10 +1,10 @@
 {% if tasks %}
     <div class="downloads-grid">
         {% for task in tasks %}
-            <div class="download-item status-{{ task.status }}">
+            <div class="download-item status-{{ task.status.value }}">
                 <div class="download-info">
                     <span class="download-name" title="{{ task.filename }}">{{ task.filename }}</span>
-                    <span class="badge badge-{{ task.status }}">{{ task.status | upper }}</span>
+                    <span class="badge badge-{{ task.status.value }}">{{ task.status | upper }}</span>
                 </div>
                 
                 <div class="progress-container">