🛡️ Sentinel: [CRITICAL] Fix insecure random number generation

[thirdeyenation]

🚨 Severity: CRITICAL
💡 Vulnerability: The codebase was using the non-cryptographic random.choices() to generate the root password for SSH and internal identifiers (generate_id()). The random module produces predictable sequences which can be guessed or reverse-engineered by an attacker.
🎯 Impact: Predictable passwords could allow an attacker to bypass authentication and gain unauthorized root access. Predictable internal identifiers could lead to insecure direct object references or unauthorized access to agent contexts.
🔧 Fix: Replaced the vulnerable random.choices() calls with the cryptographically secure secrets.choice() function from the built-in secrets module in prepare.py, helpers/guids.py, and agent.py.
✅ Verification: Verified changes locally using python3 -m py_compile on modified files, and checked for proper functionality. Added an entry to .jules/sentinel.md noting the vulnerability and prevention steps.

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PR created automatically by Jules for task 2991336506491387026 started by @thirdeyenation

[google-labs-jules]

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