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/accessible-emoji.md

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+# jsx-a11y/accessible-emoji
+
+❌ This rule is deprecated.
+
+<!-- end auto-generated rule header -->
+
+Emoji have become a common way of communicating content to the end user. To a person using a screen reader, however, they may not be aware that this content is there at all. By wrapping the emoji in a `<span>`, giving it the `role="img"`, and providing a useful description in `aria-label`, the screen reader will treat the emoji as an image in the accessibility tree with an accessible name for the end user.
+
+## Rule details
+
+This rule takes no arguments.
+
+### Succeed
+```jsx
+<span role="img" aria-label="Snowman">&#9731;</span>
+<span role="img" aria-label="Panda">🐼</span>
+<span role="img" aria-labelledby="panda1">🐼</span>
+```
+
+### Fail
+```jsx
+<span>🐼</span>
+<i role="img" aria-label="Panda">🐼</i>
+```
+
+## Accessibility guidelines
+- [WCAG 1.1.1](https://www.w3.org/WAI/WCAG21/Understanding/non-text-content.html)
+
+### Resources
+- [Léonie Watson, Accessible Emoji](https://tink.uk/accessible-emoji/)