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-alias-methods.md

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+# Disallow alias methods (`no-alias-methods`)
+
+Several Jest methods have alias names, such as `toThrow` having the alias of
+`toThrowError`. This rule ensures that only the canonical name as used in the
+Jest documentation is used in the code. This makes it easier to search for all
+occurrences of the method within code, and it ensures consistency among the
+method names used.
+
+## Rule details
+
+This rule triggers a warning if the alias name, rather than the canonical name,
+of a method is used.
+
+### Default configuration
+
+The following patterns are considered warnings:
+
+```js
+expect(a).toBeCalled();
+expect(a).toBeCalledTimes();
+expect(a).toBeCalledWith();
+expect(a).lastCalledWith();
+expect(a).nthCalledWith();
+expect(a).toReturn();
+expect(a).toReturnTimes();
+expect(a).toReturnWith();
+expect(a).lastReturnedWith();
+expect(a).nthReturnedWith();
+expect(a).toThrowError();
+```
+
+The following patterns are not considered warnings:
+
+```js
+expect(a).toHaveBeenCalled();
+expect(a).toHaveBeenCalledTimes();
+expect(a).toHaveBeenCalledWith();
+expect(a).toHaveBeenLastCalledWith();
+expect(a).toHaveBeenNthCalledWith();
+expect(a).toHaveReturned();
+expect(a).toHaveReturnedTimes();
+expect(a).toHaveReturnedWith();
+expect(a).toHaveLastReturnedWith();
+expect(a).toHaveNthReturnedWith();
+expect(a).toThrow();
+```