GHSA-4mr5-g6f9-cfrh: PraisonAI vulnerable to sandbox escape via `print.__self__` builtins module leak in `execute_code` (subprocess mode)

PraisonAI's `execute_code()` function has a critical sandbox escape vulnerability that allows attackers to execute arbitrary commands on the host system. The vulnerability exploits four gaps in security validation: the `__self__` attribute (which retrieves the real Python builtins module) is not blocked, the `vars()` function is not restricted, attribute-based function calls bypass checks, and string concatenation bypasses string constant filters. An attacker can use these gaps to access the `__import__` function and run OS commands, completely defeating the sandbox protection.