Security: Implement token encryption for file-based storage

[knowlen]

Description

As identified in PR #32 review, the current file-based token storage implementation uses proper file permissions but lacks encryption at rest. This could be enhanced for better security.

Current State

• Tokens are stored in plain JSON files (.esologs_token.json)
• File permissions provide basic protection
• No encryption at rest

Proposed Solution

1. Add optional encryption using the cryptography library
2. Integrate with OS keychains using the keyring library
3. Provide configuration option to enable/disable encryption
4. Maintain backward compatibility with existing token files

Implementation Ideas

# Optional encryption wrapper
class EncryptedTokenStorage:
    def __init__(self, key_source='environment'):
        self.cipher = self._initialize_cipher(key_source)
    
    def save_token(self, token, filepath):
        encrypted_data = self.cipher.encrypt(json.dumps(token))
        # Save encrypted data
    
    def load_token(self, filepath):
        # Load and decrypt

Benefits

• Enhanced security for stored credentials
• Compliance with security best practices
• Optional feature maintains simplicity for development

Considerations

• Should be opt-in to avoid breaking existing workflows
• Clear documentation on key management
• Performance impact should be minimal

References

• PR Release v0.2.0b1 - First Beta Release #32 review feedback
• Security best practices for credential storage