feat(cloud-api): Add Corgea AI fixer integration (Tier 2.5)

- Add Corgea fixer for AI-generated security fixes
- Add SARIF converter for scan result upload
- Add API orchestrator for cloud fixer management
- Add integration tests for Corgea workflow
- Support PRO/ENTERPRISE tier gating

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: alpsla