Restructure project and integrate mush installation flow

[francescobianco]

This pull request includes a major refactoring of the codebase and introduces a more structured layout for the mush project.

✅ Changes

• Refactored source files for improved readability and maintainability
• Introduced a modular structure following common conventions
• Integrated the installation and execution flow directly into the project layout

🧪 How to Test (Fork Instructions)

You can test the current version of the project in this fork by following these simple steps:

1. Install MUSH
   Run the following command to install mush:

   curl get.javanile.org/mush | bash -

2. Install TPKG (from the fork)
   Once mush is installed, install the Matrix digital rain effect theme:

   mush install tpkg

3. Run the TPKG
   Enjoy the digital rain effect by running:

   tpkg -h

💻 Compatibility

This version has been tested on modern Unix-based systems and should work out-of-the-box on macOS and most Linux distributions.