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/eslint/messages/extend-config-missing.js

@@ -0,0 +1,13 @@
+"use strict";
+
+module.exports = function(it) {
+    const { configName, importerName } = it;
+
+    return `
+ESLint couldn't find the config "${configName}" to extend from. Please check that the name of the config is correct.
+
+The config "${configName}" was referenced from the config file in "${importerName}".
+
+If you still have problems, please stop by https://eslint.org/chat/help to chat with the team.
+`.trimStart();
+};