🛡️ Sentinel: [MEDIUM] Replace random with secrets for secure generation

[thirdeyenation]

🚨 Severity: MEDIUM
💡 Vulnerability: Weak random number generation for security purposes. The random module was being used to generate a root password and internal identifiers, which is not cryptographically secure and predictable.
🎯 Impact: Predictability of generated passwords or identifiers.
🔧 Fix: Replaced random.choices with secrets.choice from the built-in secrets library across prepare.py, agent.py, and helpers/guids.py.
✅ Verification: Code logic was verified, and basic syntax and execution was tested.

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PR created automatically by Jules for task 17331636551473080806 started by @thirdeyenation

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