I would like you to create a sample plugin called 'featured-posts' that includes all the necessary functionality. The goal is to develop a simple WordPress plugin that allows site administrators to select and display a list of featured posts on their website. The plugin should be easy to install and configure, and allow administrators to select featured posts through the WordPress admin panel. The requirements are as follows: Create a WordPress plugin that includes a widget and shortcode to display featured posts. The plugin should provide a section in the WordPress admin panel where administrators can select the posts they want to feature. They should be able to select posts by searching by title or ID, or by selecting from a list of recent posts. The list of featured posts should be displayed in an attractive and responsive layout, adapting to different devices and screen sizes. Administrators should have the option to display only the title of the featured posts or also include an excerpt and a featured image. Please create multiple files to make it easy to make changes and updates.

/*
Plugin Name: Featured Posts
Plugin URI: http://example.com/plugin
Description: A WordPress plugin that allows administrators to select and display a list of featured posts.
Version: 1.0
Author: Your Name Here
Author URI: http://example.com
License: GPLv2 or later
*/