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/psl/vite.config.js

@@ -0,0 +1,20 @@
+import { resolve } from 'node:path';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+  build: {
+    target: 'es2015',
+    lib: {
+      entry: resolve(__dirname, 'index.js'),
+      name: 'psl',
+      formats: ['es', 'cjs', 'umd'],
+      fileName: format => (
+        format === 'umd'
+          ? 'psl.umd.cjs'
+          : format === 'cjs'
+            ? 'psl.cjs'
+            : 'psl.mjs'
+      ),
+    },
+  },
+});