Modularize WYSIWYG Plugin Next

This is the separate, hardening-focused copy of the current WYSIWYG plugin.
Keep the existing wysiwyg_plugin folder in place until this version is proven ready to replace it.

Upload this folder to:
/home/haid/public_html/modularize/plugins/wysiwyg_plugin_next/

Assign in Modularize as:
wysiwyg_plugin_next/index.php

Files:
- index.php: Modularize adapter and HTML feed publisher.
- wysiwyg-editor.php: reusable PHP renderer.
- standalone-test.php: isolated test harness outside Modularize.
- assets/wysiwyg-editor.js: editor core and tool plugins.
- assets/wysiwyg-editor.css: editor styling.

First hardening changes in this copy:
- Added standalone-test.php so the editor can be tested without Modularize.
- Renamed plugin metadata/default paths to WYSIWYG Editor Next / wysiwyg_plugin_next.
- Added public API helpers to the editor instance:
  - focus()
  - onChange(callback)
  - emitChange(reason)
  - insertHtmlAtSelection(html)
  - replaceSelectionWithHtml(html)
  - destroy()
- Changed the main editor event bindings to use an internal cleanup path so destroy() can remove core listeners.

Editable configuration is declared in index.php under config_schema/default_config.
Modularize reads that metadata and displays it from the panel P Menu > Plugin Config.
