fix(funkwhale): assert the sign-in offer on Funkwhale, not on the logout page

The spec signed out and then asserted, on whatever page it had landed on, that
Funkwhale offers sign-in again. That page is never Funkwhale.

Both exits leave the app by design. The fallback navigates to
${appBaseUrl}/logout, but on every app vhost that exact path belongs to the
universal-logout service: roles/web-svc-logout/templates/logout-proxy.conf.j2
defines `location = /logout` with a proxy_pass, included through
sys-front-inj-all into the shared vhost. The in-app control is no better --
initLogoutPatch rewrites it to Keycloak's end-session URL with redirect_uri set
to the primary domain.

Measured in the run's trace rather than inferred:

  https://audio.infinito.example/logout   200, content-length 25
  body                                    "You have been logged out."
  clear-site-data                         "cache","cookies","storage"
  set-cookie                              sessionid=, csrftoken=, _oauth2_proxy=,
                                          _pk_* -- all Expires 1970, across the
                                          bare, app and parent domain scopes

So the sign-out itself works; the session really is gone. Only the assertion sat
on the wrong page, where no sign-in affordance can appear at any timeout.

Returning to appBaseUrl before the expectation puts the claim where it can be
true or false: the app, freshly anonymous. The locator is untouched -- 8aaac027d
and bfe7741c6 already settled how signInAffordance matches Funkwhale's bare-div
control, and this change does not revisit it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

roles/web-app-funkwhale/files/playwright/test-native-login.js

@@ -100,6 +100,8 @@ for (const persona of PERSONAS) {
       await gotoOnion(page, `${appBaseUrl}/logout`, { waitUntil: "domcontentloaded" });
     }
 
+    await gotoOnion(page, appBaseUrl, { waitUntil: "domcontentloaded" });
+
     await expect(
       signInAffordance(page),
       `after sign-out Funkwhale must offer sign-in to ${persona.label} again`,