refactor: restore root-level development workflow with enhanced tooling

- Add root package.json with development scripts and dependencies
- Move scripts/ from lib back to root for intuitive developer experience
- Clean lib/package.json to contain only runtime dependencies
- Add comprehensive justfile with cross-platform command shortcuts
- Update README.md with new development workflow instructions
- Maintain lib as clean, publishable package while enabling root-level commands

.gitignore

@@ -73,4 +73,4 @@ insertr-cli/build-errors.log
 .local/
 
 # Demo site generated files
-demo-site/insertr.js
+demo-site/insertr.js# Node.js root dependencies