fix: return empty object for configurable fields without type in simulation

When a schema has `configurable: true` but no explicit type (like `type Context any`),
return an empty object `{}` instead of `null` during data simulation.

This fixes the LLM tools `get_node_port_schema` returning `context: null` for downstream
ports when the Context field hasn't been extended with a schema yet.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Maksym Trofimenko

pkg/jsonschemagenerator/generator.go

@@ -76,7 +76,17 @@ func (se *JSONSchemaBasedDataGenerator) Generate(node *ajson.Node, clb Callback)
 
 	switch typ {
 	case "":
-		// empty schema - nil
+		// empty schema - check for default value first
+		if d, _ := node.GetKey("default"); d != nil {
+			return d.Unpack()
+		}
+		// check if configurable (can hold any user-defined data)
+		configurable, _ := GetStrKey("configurable", node)
+		if configurable == "true" {
+			// Configurable fields without type should return empty object, not null
+			// This represents "user can configure this to any value"
+			return map[string]interface{}{}, nil
+		}
 		return nil, nil
 	case "string", "number", "integer":
 		return getDefaultValue(typ, node)