OECD AI Risk Framework Integration

## Description

Implement OECD AI Principles alignment into FairMind's risk and compliance engine. This consolidates the previous OECD issues (#67-74) into a single tracked effort.

## Scope

- [ ] Risk register — structured storage for identified AI risks, mapped to OECD principles
- [ ] Automated risk analysis — scoring engine that evaluates models against OECD dimensions (transparency, accountability, robustness, fairness, safety)
- [ ] Cross-border risk assessment — flag regulatory differences across jurisdictions
- [ ] Risk analytics and reporting — dashboard visualizations and exportable reports
- [ ] API endpoints — backend services for risk CRUD, scoring, and report generation
- [ ] Testing — unit and integration tests for scoring logic and API
- [ ] Documentation — contributor guide for extending the framework

## Context

Overlaps with #149 (AI Risk - IBM/MIT integration). The OECD framework should be implemented as an additional taxonomy within the same risk assessment architecture, not a parallel system.

## Previous Issues

Consolidates: #67, #68, #69, #70, #71, #72, #73, #74