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/account.ts

@@ -12,7 +12,7 @@ import { generateSecret, otpauthUrl, parseOtpauthUrl, verifyTotp } from "./totp.
  * the registry is known to be there.
  */
 
-const STALWART_CAP = "urn:stalwart:jmap";
+const STALWART_CAP = "urn:inbuxa:jmap:registry";
 const JMAP_CORE = "urn:ietf:params:jmap:core";
 /** Stalwart's id for a singleton object; the number it encodes spells this. */
 const SINGLETON = "singleton";