Senior Engineer for VoiceCast Audio App

We are building VoiceCast — a mobile-first social audio app (live moderated rooms + short VoiceStories + real-time transcription + tipping). We need a senior full-stack engineer (or small team) experienced in WebRTC-based audio apps, realtime systems, and mobile apps (React Native OR native iOS/Android).

Must have:
- Hands-on WebRTC experience (SFU experience: LiveKit/Agora/Jitsi/Twilio)
- Experience integrating real-time STT (Deepgram/AssemblyAI/Google)
- Implemented signalled rooms, roles (host/moderator/speaker/listener)
- Payment integrations (Stripe + optional local gateways)
- CI/CD, Docker, basic infra (AWS, S3, Redis, PostgreSQL)
- Good English communication, disciplined about milestones & docs

Deliverables:
- Production-ready backend & APIs (OpenAPI)
- Mobile apps (iOS & Android builds) or React Native app
- Web client (React) with public player for VoiceStories
- Deployment scripts & documentation

Please share:
- Portfolio of similar projects (WebRTC/audio apps)
- Preferred stack and vendor recommendations
- Estimated timeline & fixed-price quote for MVP per milestone