Create RubyGem project `psdk-cli` using Thor structure

[AerunDev]

Description

As a developer or user, I want to be able to install psdk-cli via RubyGems and have an executable (psdk-cli) usable from the terminal, so that I can access Pokémon SDK commands.

Acceptance criteria

• The project follows the standard Ruby gem structure.
• The psdk-cli executable is globally accessible after installation.
• The executable displays a basic help generated by Thor.
• The source code is organized to support multiple subcommands.