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/istanbul-lib-report/lib/report-base.js

@@ -0,0 +1,16 @@
+'use strict';
+
+// TODO: switch to class private field when targetting node.js 12
+const _summarizer = Symbol('ReportBase.#summarizer');
+
+class ReportBase {
+    constructor(opts = {}) {
+        this[_summarizer] = opts.summarizer;
+    }
+
+    execute(context) {
+        context.getTree(this[_summarizer]).visit(this, context);
+    }
+}
+
+module.exports = ReportBase;