fix: return undefined for optional arrays instead of empty arrays

- Update generateDefaultValue to return undefined for optional array parameters
- Add comprehensive tests for required vs non-required arrays
- Fixes issue where MCP Inspector sends empty arrays [] for optional parameters
- Resolves compatibility issues with OpenAPI servers expecting omitted optionals

Refs #771

client/src/utils/schemaUtils.ts

@@ -109,7 +109,7 @@ export function generateDefaultValue(
     case "boolean":
       return isRequired ? false : undefined;
     case "array":
-      return [];
+      return isRequired ? [] : undefined;
     case "object": {
       if (!schema.properties) return {};