refactor(practice) - Add CTF challenge resource

[passandscore]

The Solidity-Challenges repo offers a wide range of challenges, from language-specific tasks to exploit-focused scenarios.

Checklist

• The URL is not already present in the list (check with CTRL/CMD+F in the raw markdown file).
• Each description starts with an uppercase character and ends with a period.
  Example: solc-js - JavaScript bindings for the compiler.
• Drop all A / An prefixes at the start of the description.
• Avoid using the word Solidity in the description.