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/argparse/lib/const.js

@@ -0,0 +1,21 @@
+//
+// Constants
+//
+
+'use strict';
+
+module.exports.EOL = '\n';
+
+module.exports.SUPPRESS = '==SUPPRESS==';
+
+module.exports.OPTIONAL = '?';
+
+module.exports.ZERO_OR_MORE = '*';
+
+module.exports.ONE_OR_MORE = '+';
+
+module.exports.PARSER = 'A...';
+
+module.exports.REMAINDER = '...';
+
+module.exports._UNRECOGNIZED_ARGS_ATTR = '_unrecognized_args';