build: declare @quantus/crypto as a ui-keyring dev dependency

The ML-DSA restore spec imports contextForSpec from it, and polkadot-dev's
build refuses a package whose sources import something undeclared.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uDUodEcRbBwNRi3UCmw8f

yarn.lock

@@ -1696,6 +1696,7 @@ __metadata:
     "@polkadot/ui-settings": "npm:3.16.7"
     "@polkadot/util": "npm:^14.0.3"
     "@polkadot/util-crypto": "npm:14.0.3-quantus.3"
+    "@quantus/crypto": "npm:^0.3.0"
     "@types/mkdirp": "npm:^2.0.0"
     "@types/store": "npm:^2.0.5"
     mkdirp: "npm:^3.0.1"