v4.2: Improved Audit & Activity Log

Relevant system and content changes must be traceable for compliance and operational transparency.

Scope
- Content changes
- Role and permission changes
- Security-relevant actions

Acceptance Criteria
- All relevant actions are logged
- Logs are filterable and exportable
- Logs are tamper-resistant
- Retention policies are configurable
- GDPR-compliant operation is possible
