Add dynamic nested form preview

[krunal811]

Summary

• create a new FormPreview component that renders inputs from a form configuration object
• support field validation and nested containers (tabs, columns, panels)
• update preview modal to use the new interactive preview
• add a home page with saved forms and route-based navigation
• persist forms to local storage with load/save helpers
• integrate React Router and add a link back to Home

Testing

• npm run lint (fails: ESLint couldn't find a configuration file)