Ensure roomId are not rendered in the UI.

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Use RoomAvatar data fallback everywhere, to not use roomId (`!` char) for the avatar initial, but rather `#`.

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/components/avatar/AvatarData.kt

@@ -26,7 +26,8 @@ data class AvatarData(
     val size: AvatarSize,
 ) {
     val initial by lazy {
-        (name?.takeIf { it.isNotBlank() } ?: id)
+        // For roomIds, use "#" as initial
+        (name?.takeIf { it.isNotBlank() } ?: id.takeIf { !it.startsWith("!") } ?: "#")
             .let { dn ->
                 var startIndex = 0
                 val initial = dn[startIndex]