Use the server's renamed registry capability, urn:inbuxa:jmap:registry

inbuxa-server renames the identifiers that carried the upstream name (its
SPEC.md §2.4). Upstream's capability for the registry (x:) objects is now
urn:inbuxa:jmap:registry, beside the fork's own urn:inbuxa:jmap, which is
unchanged. There's no alias, so this lands with the server change and
deploys with it. The mock advertises the new name too. No user-visible
strings change.

server/src/login-guard.test.ts

@@ -18,7 +18,7 @@ const PORT = 18799;
 process.env.MOCK_PORT = String(PORT);
 process.env.MOCK_USER = "[email protected]";
 process.env.MOCK_PASS = "demo-password";
-process.env.MOCK_NO_REGISTRY = "1"; // a server without urn:stalwart:jmap
+process.env.MOCK_NO_REGISTRY = "1"; // a server without urn:inbuxa:jmap:registry
 process.env.MAIL_SERVER_URL = `http://127.0.0.1:${PORT}`;
 process.env.APP_SECRET = "test-secret-for-login-guard";