Fix: Update build and dependencies for React 18, webpack 5, and react-select v5 compatibility (#154)

[VictorIvanov87]

This PR addresses issue #154 by upgrading the plugin’s dependencies and build tooling for compatibility with React 18, webpack 5, and react-select v5.

Key changes include:

• Upgraded React and ReactDOM to v18
• Updated all @wordpress/* packages to latest versions compatible with React 18
• Upgraded @humanmade/webpack-helpers to a webpack 5-compatible version
• Updated PostCSS and related loaders for webpack 5 support
• Replaced deprecated react-sortable-hoc with @dnd-kit/sortable
• Refactored react-select usage to v5, resolving ESM import errors with @floating-ui/dom
• Removed legacy and incompatible plugins (e.g., bell-on-bundler-error-plugin)
• Ensured asset manifest naming matches PHP loader expectations

These changes resolve build errors, eliminate React warnings, and ensure the plugin works with modern WordPress and JavaScript tooling.