Fix icon build process and README

- Update gulpfile to copy PNG files to dist
- Remove broken image link from README
- Rebuild with PNG icon included

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

gulpfile.js

@@ -1,7 +1,7 @@
 const { src, dest } = require('gulp');
 
 function buildIcons() {
-	return src('nodes/**/*.svg').pipe(dest('dist/nodes'));
+	return src('nodes/**/*.{svg,png}').pipe(dest('dist/nodes'));
 }
 
 exports['build:icons'] = buildIcons;