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/core-js-compat/index.d.ts

@@ -0,0 +1,27 @@
+import type compat from './compat'
+import type getModulesListForTargetVersion from './get-modules-list-for-target-version';
+import type { ModuleName, Target, TargetVersion } from './shared'
+
+type CompatData = {
+  [module: ModuleName]: {
+    [target in Target]?: TargetVersion
+  }
+};
+
+declare const ExportedCompatObject: typeof compat & {
+  compat: typeof compat,
+
+  /** The subset of modules which available in the passed `core-js` version */
+  getModulesListForTargetVersion: typeof getModulesListForTargetVersion,
+
+  /** Full list compatibility data */
+  data: CompatData,
+
+  /** map of modules by `core-js` entry points */
+  entries: {[entry_point: string]: readonly ModuleName[]},
+
+  /** Full list of modules */
+  modules: readonly ModuleName[]
+}
+
+export = ExportedCompatObject