Add the webrtc dependency that the in-core RTC transport will use. Verified
it cross-compiles to aarch64-apple-ios, confirming RTC can live in the shared
core and reach every native platform from one implementation (the browser
keeps native RTCPeerConnection and interops over the wire).
Also fix a latent bug: the SSE transport forwarded every message type to the
sink, so a peer's presence/signal chirps would leak into the clipboard feed.
Now SSE forwards only clipboard; presence/signal belong to the RTC layer.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Patrick Ecord
a700a4b54b
