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-jest/docs/rules/no-jasmine-globals.md

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+# Disallow Jasmine globals (`no-jasmine-globals`)
+
+`jest` uses `jasmine` as a test runner. A side effect of this is that both a
+`jasmine` object, and some jasmine-specific globals, are exposed to the test
+environment. Most functionality offered by Jasmine has been ported to Jest, and
+the Jasmine globals will stop working in the future. Developers should therefore
+migrate to Jest's documented API instead of relying on the undocumented Jasmine
+API.
+
+### Rule details
+
+This rule reports on any usage of Jasmine globals which is not ported to Jest,
+and suggests alternative from Jest's own API.
+
+### Default configuration
+
+The following patterns are considered warnings:
+
+```js
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 5000;
+
+test('my test', () => {
+  pending();
+});
+
+test('my test', () => {
+  fail();
+});
+
+test('my test', () => {
+  spyOn(some, 'object');
+});
+
+test('my test', () => {
+  jasmine.createSpy();
+});
+
+test('my test', () => {
+  expect('foo').toEqual(jasmine.anything());
+});
+```
+
+The following patterns would not be considered warnings:
+
+```js
+jest.setTimeout(5000);
+
+test('my test', () => {
+  jest.spyOn(some, 'object');
+});
+
+test('my test', () => {
+  jest.fn();
+});
+
+test('my test', () => {
+  expect('foo').toEqual(expect.anything());
+});
+```