open-webui: SSO via authentik (OIDC authorization-code flow)

- quadlet: OAUTH_*/OPENID_* env + EnvironmentFile for the client secret
  (secret stays off-repo in /home/dank/Containers/open-webui/env, mode 600)
- authentik objects created live: application 'open-webui', OAuth2 provider
  'Open WebUI' (Strict redirect URI), 'Open WebUI roles' scope mapping,
  entitlements Open WebUI Users/Admins bound to openwebui_users/admins
- e2e: 18-openwebui-sso.spec.ts (silent SSO round-trip) + prefix in config
- unit tests: OIDC wiring + secret-hygiene assertions
- docs: SSO section + history entry

tests/e2e/playwright.config.ts

@@ -28,8 +28,9 @@ export default defineConfig({
       // whose prefix is not listed in any project silently never runs — a
       // 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).
-      testMatch: /(10|12|13|16|17)-.*\.spec\.ts/,
+      // 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/,
       use: { storageState: ".auth/qa-e2e.json" },
       dependencies: ["setup"],
     },