Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/ajv-keywords/keywords/_util.js

@@ -0,0 +1,15 @@
+'use strict';
+
+module.exports = {
+  metaSchemaRef: metaSchemaRef
+};
+
+var META_SCHEMA_ID = 'http://json-schema.org/draft-07/schema';
+
+function metaSchemaRef(ajv) {
+  var defaultMeta = ajv._opts.defaultMeta;
+  if (typeof defaultMeta == 'string') return { $ref: defaultMeta };
+  if (ajv.getSchema(META_SCHEMA_ID)) return { $ref: META_SCHEMA_ID };
+  console.warn('meta schema not defined');
+  return {};
+}