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/v8-to-istanbul/index.d.ts

@@ -0,0 +1,25 @@
+/// <reference types="node" />
+
+import { Profiler } from 'inspector'
+import { CoverageMapData } from 'istanbul-lib-coverage'
+import { RawSourceMap } from 'source-map'
+
+declare type Sources =
+  | {
+      source: string
+    }
+  | {
+      source: string
+      originalSource: string
+      sourceMap: { sourcemap: RawSourceMap }
+    }
+declare class V8ToIstanbul {
+  load(): Promise<void>
+  destroy(): void
+  applyCoverage(blocks: ReadonlyArray<Profiler.FunctionCoverage>): void
+  toIstanbul(): CoverageMapData
+}
+
+declare function v8ToIstanbul(scriptPath: string, wrapperLength?: number, sources?: Sources, excludePath?: (path: string) => boolean): V8ToIstanbul
+
+export = v8ToIstanbul