fix: initialize SHA-512 hash function for @noble/ed25519 v3

@noble/ed25519 v3.0.0 requires explicit SHA-512 hash function setup
before using any cryptographic operations. This fixes the
"hashes.sha512 not set" error.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@xtr-dev/rondevu-client",
-  "version": "0.8.1",
+  "version": "0.8.2",
   "description": "TypeScript client for Rondevu DNS-like WebRTC with username claiming and service discovery",
   "type": "module",
   "main": "dist/index.js",

src/usernames.ts

@@ -1,5 +1,11 @@
 import * as ed25519 from '@noble/ed25519';
 
+// Set SHA-512 hash function for ed25519 (required in @noble/ed25519 v3+)
+// Uses built-in WebCrypto API
+ed25519.hashes.sha512Async = async (message: Uint8Array) => {
+  return new Uint8Array(await crypto.subtle.digest('SHA-512', message as BufferSource));
+};
+
 /**
  * Username claim result
  */