[SloMR]

Summary

This adds unit tests for the signaling state machine on both clients: the same six checks on iOS and the web, each covering a failure we have hit before. To make that possible, signaling now gets its WebSocket, TURN, WebRTC and timer dependencies from outside, and the web moves from Karma to Vitest. The apps behave as before, except that the web now drops a peer's queued frames when it gives up on that peer, as iOS already does. The signaling logic itself is otherwise unchanged.

What changed

• SignalingService on iOS takes its WebSocket, TURN source, WebRTC calls and clock through init (SignalTransport, IceServerSource, WebRTCEngine, any Clock<Duration>), and the app passes the real ones
• iOS channel and ICE state handling moves out of the delegate methods into handleChannelState(_:onChannel:) and handleIceState(_:onConnection:)
• The iOS app stays offline while it hosts the unit tests (AppBuildInfo.isRunningTests)
• iOS unit tests use Swift Testing and swift-clocks, and CI runs them on an iPhone simulator
• The web runs its unit tests on Vitest with jsdom instead of Karma in Chrome, and its builders move to @angular/build
• The web signaling service creates peer connections through PeerConnectionFactory
• Both clients name the server's WebSocket prefixes in a WebSocketPrefix enum instead of raw strings
• Six signaling tests on each client: a failed build doesn't leave a peer connecting, giving up drops queued frames, queued frames go out before newer ones, a teardown and a new attempt leave one connection, a retry after a close starts a new connection, and a new attempt cancels the old retry
• The web drops a peer's queued frames when it gives up on that peer