Security audit and hardening

[krjordan]

Perform security review and implement hardening measures.

Requirements

• Review MQTT TLS implementation
• Audit file permissions and storage
• Validate all user inputs
• Secure credential storage
• Address dependency vulnerabilities

Acceptance Criteria

• MQTT uses proper TLS verification
• Config files have appropriate permissions
• All inputs validated and sanitized
• Credentials stored securely
• No high/critical CVEs in dependencies
• Security best practices documented