Integrate External Threat Feeds

## Description\nConnect to external threat intelligence feeds for enhanced security.\n\n**Acceptance Criteria:**\n- Support for common threat feed formats\n- Scheduled updates\n- Threat matching\n- Alerting

No files, tests, feed providers, supported formats, scheduling mechanism, matching rules, or alerting entry points are identified. First map the repository's existing API security and integration surfaces, then clarify those implementation choices. Done means the agreed feeds update on schedule, threats are matched, and alerts are emitted with testable acceptance criteria.

由索引模型根据 Issue 内容生成。