New ringing UI

This implements the new ringing UI by showing a placeholder tile for the participant being dialed, rather than an overlay.

src/state/media/RingingMediaViewModel.ts

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+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type Behavior } from "../Behavior";
+import { type MuteStates } from "../MuteStates";
+import {
+  type BaseMediaInputs,
+  type BaseMediaViewModel,
+  createBaseMedia,
+} from "./MediaViewModel";
+
+/**
+ * Media representing a user who is not yet part of the call — one that we are
+ * *ringing*.
+ */
+export interface RingingMediaViewModel extends BaseMediaViewModel {
+  type: "ringing";
+  pickupState$: Behavior<"ringing" | "timeout" | "decline">;
+  /**
+   * Whether this media would be expected to have video, were it not simply a
+   * placeholder.
+   */
+  videoEnabled$: Behavior<boolean>;
+}
+
+export interface RingingMediaInputs extends BaseMediaInputs {
+  pickupState$: Behavior<"ringing" | "timeout" | "decline">;
+  /**
+   * The local user's own mute states.
+   */
+  muteStates: MuteStates;
+}
+
+export function createRingingMedia({
+  pickupState$,
+  muteStates,
+  ...inputs
+}: RingingMediaInputs): RingingMediaViewModel {
+  return {
+    ...createBaseMedia(inputs),
+    type: "ringing",
+    pickupState$,
+    // If our own video is enabled, then this is a video call and we would
+    // expect remote media to have video as well
+    videoEnabled$: muteStates.video.enabled$,
+  };
+}