feat(share): share user permalinks via to.healthchat.ch

Mention pills keep the matrix.to wire format other clients expect.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/permalink/PermalinkBuilder.kt

@@ -28,6 +28,16 @@ interface PermalinkBuilder {
      * @param roomAlias the room alias to link to.
      */
     fun permalinkForRoomAlias(roomAlias: RoomAlias): Result<String>
+
+    /**
+     * Permalink meant to be shared outside of Matrix, for instance through the system share sheet.
+     * It points to the HealthChat matrix.to deployment, so that recipients who do not have the app
+     * yet are offered HealthChat rather than Element.
+     *
+     * Links embedded in events (mention pills, replies, …) must keep using [permalinkForUser]:
+     * matrix.to is the format other Matrix clients expect on the wire.
+     */
+    fun sharePermalinkForUser(userId: UserId): Result<String>
 }
 
 sealed class PermalinkBuilderError : Throwable() {