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-jsx-a11y/docs/rules/click-events-have-key-events.md

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+# jsx-a11y/click-events-have-key-events
+
+💼 This rule is enabled in the following configs: ☑️ `recommended`, 🔒 `strict`.
+
+<!-- end auto-generated rule header -->
+
+Enforce `onClick` is accompanied by at least one of the following: `onKeyUp`, `onKeyDown`, `onKeyPress`. Coding for the keyboard is important for users with physical disabilities who cannot use a mouse, AT compatibility, and screen reader users. This does not apply for interactive or hidden elements.
+
+## Rule details
+
+This rule takes no arguments.
+
+### Succeed
+```jsx
+<div onClick={() => {}} onKeyDown={this.handleKeyDown} />
+<div onClick={() => {}} onKeyUp={this.handleKeyUp} />
+<div onClick={() => {}} onKeyPress={this.handleKeyPress} />
+<button onClick={() => {}} />
+<div onClick{() => {}} aria-hidden="true" />
+```
+
+### Fail
+```jsx
+<div onClick={() => {}} />
+```
+
+## Accessibility guidelines
+- [WCAG 2.1.1](https://www.w3.org/WAI/WCAG21/Understanding/keyboard)