Add peer card discovery scaffold

crates/geth-auth/src/lib.rs

@@ -71,6 +71,18 @@ impl AuthExplanation {
             evaluated_ops: 0,
         }
     }
+
+    #[must_use]
+    pub fn discovered_candidate(subject: String, resource: String, capability: String) -> Self {
+        Self {
+            subject,
+            resource,
+            capability,
+            allowed: false,
+            reason: "subject is a discovered peer candidate only; discovery does not grant trust or authorization".to_owned(),
+            evaluated_ops: 0,
+        }
+    }
 }
 
 #[cfg(test)]