Add BlackVault — Open-source proxy gateway for AI API keys

## BlackVault

**GitHub:** https://github.com/venkat22022202/black-vault
**Live Demo:** https://black-vault-murex.vercel.app
**License:** MIT

### Description

Open-source proxy gateway for AI API keys. Instead of sharing real API keys with AI agents, generate proxy tokens. BlackVault injects the real key server-side and forwards to OpenAI, Anthropic, or Google AI with full SSE streaming.

Kill a token = instant 401. No key rotation needed.

### Features
- AES-256-GCM encrypted vault
- Proxy gateway with SSE streaming (OpenAI, Anthropic, Google AI)
- Instant kill switch
- Per-session cost tracking
- Activity audit trail
- Self-hostable, MIT licensed

### Tech
Next.js 16 · TypeScript · tRPC · Drizzle ORM · Neon Postgres · Upstash Redis