feat: wire QUIC transport, JNI bridge, connect UI + add docs
- Replace raw FFI with proper `jni` crate for string marshalling
- Wire QUIC transport in engine: connect to relay, crypto handshake
(CallOffer/CallAnswer, X25519+Ed25519), send/recv MediaPackets
- Feed received packets into jitter buffer (was previously ignored)
- Add connect screen UI with CALL button (idle state) and in-call
controls (mute, speaker, hang up, live stats)
- Hardcode relay 172.16.81.125:4433, room "android"
- Add comprehensive docs in docs/android/:
architecture.md (8 mermaid diagrams), build-guide.md,
debugging.md, maintenance.md, roadmap.md
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
8d5f6fe044