test(e2e): run the SvelteKit SPA Playwright suite in CI

The e2e CI job ran the legacy `scenarios/*` specs against the vanilla `static/`
frontend that upstream has since removed, so it could never pass. Point CI at
this repo's SvelteKit SPA suite (tests/e2e/spa) and wire up what it needs:

- CI: build the release binary with `--features plugins` (the admin Plugins-tab
  specs exercise the WASM runtime) and run `npm run test:coverage`, building the
  instrumented SPA with COVERAGE=1 VITE_E2E=1 so the server serves the
  data-testid-instrumented build the specs drive.
- Coverage harness: target 127.0.0.1 instead of `localhost` (which resolves to
  ::1 first on CI runners while the server binds IPv4, so readiness never
  connected) and poll `/ready` for webServer readiness; tee start-server-spa.sh
  output to a log surfaced by an always-run CI step for diagnostics.
- Files page: restore a persistent breadcrumb home link (buildCrumbs returns
  only the path folders, so there was no "go home" affordance), and fix the
  `?file=` deep-link race where the viewer→URL effect stripped the param before
  the listing loaded — a bookmarked preview link now opens the viewer.

All 101 spa specs pass locally.

tests/e2e/spa/files-extra.spec.ts

@@ -202,9 +202,11 @@ test('breadcrumb navigates back to home', async ({ page }) => {
   const folderName = uniq('Crumb');
   const folder = await apiCreateFolder(page, folderName);
   await page.goto(`/files/${folder.id}`);
-  // Breadcrumb home link returns to the root listing.
+  // Breadcrumb home link leaves the subfolder for the root listing. Bare /files
+  // canonicalizes to the user's drive root, where the just-created folder lives.
   await page.getByTestId('files-breadcrumb-home-link').click();
-  await expect(page).toHaveURL(/\/files\/?$/);
+  await expect(page).not.toHaveURL(new RegExp(folder.id));
+  await expect(page.getByTestId(folderName)).toBeVisible({ timeout: 15_000 });
 });
 
 test('open an image in the viewer and use the zoom controls', async ({ page }) => {