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-plugin-import/docs/rules/no-self-import.md

@@ -0,0 +1,32 @@
+# import/no-self-import
+
+<!-- end auto-generated rule header -->
+
+Forbid a module from importing itself. This can sometimes happen during refactoring.
+
+## Rule Details
+
+### Fail
+
+```js
+// foo.js
+import foo from './foo';
+
+const foo = require('./foo');
+```
+
+```js
+// index.js
+import index from '.';
+
+const index = require('.');
+```
+
+### Pass
+
+```js
+// foo.js
+import bar from './bar';
+
+const bar = require('./bar');
+```