Fix plugin check issues

[Zodiac1978]

If you are still interested in staying in the official directory:

In Phase 2, Plugin Check will expand to cover updates made by plugin authors to plugins already in the Directory. The initial rollout will include a post-SVN check-in process, where Plugin Check will email plugin authors about detected issues and notify Plugin Team members based on severity.

https://make.wordpress.org/plugins/2024/12/24/plugin-check-goals-roadmap/

For example:

• In footer ($in_footer) is not set explicitly wp_enqueue_script; It is recommended to load scripts in the footer. Please set this value to true to load it in the footer, or explicitly false if it should be loaded in the header.
• The "Tested up to" value in your plugin is not set to the current version of WordPress. This means your plugin will not show up in searches, as we require plugins to be compatible and documented as tested up to the most recent version of WordPress.
• $_POST['slug'] not unslashed before sanitization. Use wp_unslash() or similar
• Detected usage of a possibly undefined superglobal array index: $_POST['slug']. Use isset() or empty() to check the index exists before using it
• Processing form data without nonce verification.
• All output should be run through an escaping function (see the Security sections in the WordPress Developer Handbooks)