Fix: mock the new filter_selection_data request in Playwright e2e tests

CI (https://github.com/paperless-ngx/paperless-ngx/actions/runs/29777331059)
failed every e2e test that reloads the document list, with the browser
throwing "TypeError: Failed to fetch". Root cause: the e2e harness only
starts the Angular dev server (no real backend), and relies entirely on
page.routeFromHAR(..., { notFound: 'fallback' }) to mock API responses,
falling through to the real network for anything not in a recorded HAR.
The new GET /api/documents/filter_selection_data/ request added by this
branch fires on every non-search reload() and isn't in any pre-recorded
HAR fixture, so it fell through to a real network call with nothing
listening on the other end.

Added a shared mockFilterSelectionData() helper that stubs an empty
response for that endpoint, registered via test.beforeEach() before each
affected test's own routeFromHAR() call in every spec file that
exercises document-list reload (document-list, dashboard,
global-permissions, settings, document-detail). Playwright resolves
routes in reverse-registration order, so the later-registered HAR route
checks first, calls route.fallback() on a miss, and defers back to this
earlier-registered stub instead of hitting the network.

Not verified locally (Playwright browser binaries aren't installed in
this environment and the user preferred not to install them); relying
on CI to confirm.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src-ui/e2e/admin/settings.spec.ts

@@ -1,5 +1,10 @@
 import { expect, test } from '@playwright/test'
 import path from 'node:path'
+import { mockFilterSelectionData } from '../mock-filter-selection-data'
+
+test.beforeEach(async ({ page }) => {
+  await mockFilterSelectionData(page)
+})
 
 const REQUESTS_HAR = path.join(__dirname, 'requests/api-settings.har')