feat: SSO group autocomplete for per-host SSO allow-lists (v1.34.0)

The per-host "Allowed groups" field suggested only local groups,
permission subjects and conf.auth maps. None of those can ever match an
SSO-gated host: its allow-list is checked against the `groups` claim the
SSO issues (utils/host_sso.js), so only SSO groups are candidates.

Adds a conf.sso block (url + read-only apiToken, minted by theta-suite's
bootstrap) and a cached /api/group lookup merged into the suggestions.
Degrades silently to the previous local-only list when unset, and never
fails the request.

Authenticates with `Authorization: Bearer <token>` -- the SSO's
`auth-token` header is for browser session UUIDs and rejects a minted
API token.

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

secrets.js.example

@@ -42,6 +42,18 @@ module.exports = {
         usernameClaim: 'preferred_username',
     },
 
+    // Read-only access to the SSO's management API, used to populate the
+    // per-host SSO allow-list autocomplete with the directory's actual groups.
+    // A host gated on SSO matches its allow-list against the `groups` claim the
+    // SSO issues, so only SSO groups can ever match -- without this the field
+    // can only suggest the proxy's own local groups. `apiToken` is a machine
+    // token minted by theta-suite's bootstrap; leaving it blank simply falls
+    // back to local-only suggestions.
+    sso: {
+        url: 'http://sso-manager:3001',
+        apiToken: '',
+    },
+
     // Direct LDAP user lookups. ldaps:// + rejectUnauthorized:false for a
     // self-signed cert (the SSO's default), or set tlsOptions.ca to a CA path
     // for strict verification. bindPassword MUST match the