Emacs: complete examples for Modus themes derivatives

I just expanded the manual of the modus-themes with complete step-by-step examples on how to define a derivative theme. Here is the commit:

commit c94938ff794d043447ed4ffe9b55f1031039f667
Author: Protesilaos Stavrou <info@protesilaos.com>
Date:   Mon Nov 10 13:02:49 2025 +0200

  Greatly expand the manual with complete examples of creating Modus derivatives

  This covers the basic and more advanced use cases. It also is for both
  private use and making new packages.

 doc/modus-themes.info | 588 +++++++++++++++++++++++++++++++++++++-------------
 doc/modus-themes.org  | 278 +++++++++++++++++++++++-
 2 files changed, 711 insertions(+), 155 deletions(-)

The relevant sections and their structure:

If something is unclear, you are welcome to contact me.