ax(node): replace prose comment with usage example on safeKeyPrefix

AX Principle 2: comments show HOW with real values, not WHAT the signature says.

Co-Authored-By: Charon <charon@lethean.io>

pkg/node/peer.go

@@ -56,7 +56,8 @@ const (
 // peerNameRegex validates peer names: alphanumeric, hyphens, underscores, and spaces
 var peerNameRegex = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9\-_ ]{0,62}[a-zA-Z0-9]$|^[a-zA-Z0-9]$`)
 
-// safeKeyPrefix returns a truncated key for logging, handling short keys safely
+// safeKeyPrefix("abc123def456xyz789") // "abc123def456xyz7..."
+// safeKeyPrefix("")                   // "(empty)"
 func safeKeyPrefix(key string) string {
 	if len(key) >= 16 {
 		return key[:16] + "..."