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/indent-string/index.d.ts

@@ -0,0 +1,42 @@
+declare namespace indentString {
+	interface Options {
+		/**
+		The string to use for the indent.
+
+		@default ' '
+		*/
+		readonly indent?: string;
+
+		/**
+		Also indent empty lines.
+
+		@default false
+		*/
+		readonly includeEmptyLines?: boolean;
+	}
+}
+
+/**
+Indent each line in a string.
+
+@param string - The string to indent.
+@param count - How many times you want `options.indent` repeated. Default: `1`.
+
+@example
+```
+import indentString = require('indent-string');
+
+indentString('Unicorns\nRainbows', 4);
+//=> '    Unicorns\n    Rainbows'
+
+indentString('Unicorns\nRainbows', 4, {indent: '♥'});
+//=> '♥♥♥♥Unicorns\n♥♥♥♥Rainbows'
+```
+*/
+declare function indentString(
+	string: string,
+	count?: number,
+	options?: indentString.Options
+): string;
+
+export = indentString;