fix: enhance SSH security settings and randomize devbox password

[dinoallo]

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Pull Request Overview

This PR enhances SSH security configuration and improves password security for Docker containers across multiple OS variants. The changes replace default passwords with randomly generated ones and strengthen SSH access controls.

• Replaces hardcoded "devbox" password with randomly generated passwords using OpenSSL
• Disables SSH password authentication and restricts root login to key-based authentication only
• Updates base images to use specific versions instead of latest tags

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
OS/ubuntu/24.04/Dockerfile	Adds SSH security settings and random password generation
OS/ubuntu-cuda/24.04/Dockerfile	Applies same SSH security enhancements with password randomization
OS/debian-ssh/12.6/Dockerfile	Updates base image, adds packages, and implements security improvements

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