Add ShieldAI technical architecture and implementation plan (FRE-4459)
- System overview with 3 core services: VoicePrint, DarkWatch, SpamShield
- Tech stack: TypeScript, Fastify, Next.js, PostgreSQL, Redis, Python/FastAPI
- Build vs buy decisions for each component
- 6-phase implementation timeline (24 weeks)
- Infrastructure, security, risk mitigation, and team estimates
- API surface definitions for all services
- Child issues created: FRE-4470 through FRE-4475
Co-Authored-By: Paperclip <noreply@paperclip.ing>