⚠️ SECURITY-#203: Remove shell injection vulnerability in write_file_system

[FernandoCelmer]

Description

Remove write_file_system function that used os.system() with unsanitized string interpolation, enabling arbitrary command execution (RCE).

Issue: 📌 ISSUE-#203

Changes

• Remove write_file_system from dotflow/utils/tools.py
• Remove from os import system import
• Update tests to use write_file (safe open() based alternative)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes