Potential fix for code scanning alert no. 16: Uncontrolled command line

[whyseu]

Potential fix for https://github.com/agent-network-protocol/anp-agent-openchat/security/code-scanning/16

To fix the issue, we will validate the port value to ensure it is a valid integer and falls within the acceptable range for network ports (1–65535). This prevents malicious input from being passed to the cmd list. We'll implement a helper function validate_port to enforce these checks and update the start_instance and kill_processes_by_port functions to use this validation.

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