v4.6.0-preview.1 — WebRTC facade (preview) & Voip* config rename

⚠️ Pre-release. Ships the new WebRTC facade as a preview: it has not yet been
validated against real browsers (Chrome/Firefox) and its API may still change before it is
declared stable. The SIP stack (VoipClient) is unchanged and production-ready.

✨ Highlights

Public WebRTC facade (preview, transport-only) — a signalling-neutral browser/peer surface
in the CalloraVoipSdk.WebRtc namespace, mirroring the four-level design of VoipClient. The app
owns signalling and the codec; the SDK runs ICE, DTLS-SRTP, BUNDLE and RTP/RTCP and moves bytes —
it never encodes or decodes.

• WebRtcClient / IWebRtcClient — new WebRtcClient() or DI via AddCalloraWebRtc(...);
  CreatePeer() returns an IPeerConnection.
• Signalling happy path — peer.ConnectAsync(IWebRtcSignaling, WebRtcRole) drives the full
  RFC 8829 offer/answer over your channel and completes when connected (the WebRTC counterpart to
  DialAndWaitUntilConnectedAsync). Neutral primitives (CreateOffer / SetRemoteDescriptionAsync
  / StartAsync) remain for manual control.
• W3C track model — TrackReceived → RemoteTrack (Kind, StreamId = remote a=msid,
  TrackId) with EncodedFrame (payload, RTP timestamp, key-frame flag).
• Multi-peer manager — IWebRtcClient.Peers.
• L3 extension seams — IMediaTap + AttachMediaTap (in/out media for recording/analytics/AI);
  IWebRtcClientModule + IWebRtcClient.Modules (programmatic or DI auto-attached).
• Two-facade composition — AddCalloraVoip(sip => …).AddWebRtc(rtc => …).
• Samples — WebRtcPeer, WebRtcRecording, WebRtcDependencyInjection, and a simplest-form
  browser video-call website (WebRtcVideoCall.Web).

💥 Breaking changes

The SIP-facade configuration types were renamed so each facade owns a facade-scoped name (parallel
to WebRtcConfiguration / WebRtcOptions / AddCalloraWebRtc), freeing the Callora* names for the
upcoming composition layer. There are no compatibility aliases.

Before	After
SdkConfiguration	VoipConfiguration
SdkOptions	VoipOptions
AddCallora(...)	AddCalloraVoip(...)

Migration — rename these three symbols at your call sites:

// before
services.AddCallora(o => { /* … */ });
var cfg = new SdkConfiguration { /* … */ };

// after
services.AddCalloraVoip(o => { /* … */ });
var cfg = new VoipConfiguration { /* … */ };

VoipClient and all other public types are unchanged; behaviour is identical.

⚠️ Preview limitations

- Not yet validated against real browsers (Chrome/Firefox).
- Both peers need a configured media port until early-bind / trickle ICE lands.
- No data channels (SCTP), TURN relay or simulcast yet.

📦 Targets

net8.0 · net9.0 · net10.0

Full changelog: CHANGELOG.md (https://github.com/BechsteinDigital/CalloraVoipSDK/blob/main/CHANGELOG.md)