test(e2e): cover Grafana relying-party SSO landing (spec 20)

13-sso proves an authenticated session reaches Grafana login page but never
follows the OAuth button, so the relying-party login could be dead (500, or an
email-claim gap bouncing to /login) while the suite stayed green. Spec 20 drives
/login/generic_oauth through the real Anubis+authentik round-trip and asserts a
live session (/api/user 200 with a non-empty email). Wire 20- into the standard
project (qa-e2e session).

tests/e2e/playwright.config.ts

@@ -29,8 +29,10 @@ export default defineConfig({
       // green suite with a test that does not exist. 17- joined on 2026-09-16
       // (the hermes vhost, whose upstream is a host address rather than a
       // container name, so it needs its own pass condition). 18- joined on
-      // 2026-09-24 (OpenWebUI SSO through authentik).
-      testMatch: /(10|12|13|16|17|18)-.*\.spec\.ts/,
+      // 2026-09-24 (OpenWebUI SSO through authentik). 20- joined on 2026-10-21
+      // (Grafana's OAuth2 relying-party login, which the edge-only 13- never
+      // follows).
+      testMatch: /(10|12|13|16|17|18|20)-.*\.spec\.ts/,
       use: { storageState: ".auth/qa-e2e.json" },
       dependencies: ["setup"],
     },