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/@rushstack/eslint-patch/.eslintrc.js

@@ -0,0 +1,22 @@
+// This is a workaround for https://github.com/eslint/eslint/issues/3458
+require('decoupled-local-node-rig/profiles/default/includes/eslint/patch/modern-module-resolution');
+// This is a workaround for https://github.com/microsoft/rushstack/issues/3021
+require('decoupled-local-node-rig/profiles/default/includes/eslint/patch/custom-config-package-names');
+
+module.exports = {
+  extends: [
+    'decoupled-local-node-rig/profiles/default/includes/eslint/profile/node',
+    'decoupled-local-node-rig/profiles/default/includes/eslint/mixins/friendly-locals',
+    'decoupled-local-node-rig/profiles/default/includes/eslint/mixins/tsdoc'
+  ],
+  parserOptions: { tsconfigRootDir: __dirname },
+
+  overrides: [
+    {
+      files: ['*.ts', '*.tsx'],
+      rules: {
+        'no-console': 'off'
+      }
+    }
+  ]
+};