Ensure credentials are stored encrypted

[TooAngel]

Audit and ensure all sensitive credentials are properly encrypted in storage.

Context:

• Application handles GitHub tokens and session secrets
• Production security requires encrypted credential storage
• Need to verify current credential handling meets security standards

Acceptance Criteria:

• Audit current credential storage methods
• Verify GitHub tokens are properly encrypted
• Check session secret handling
• Review environment variable security
• Implement encryption for any plaintext credentials found
• Document credential security practices

Priority: High