fix(ui): Show delivered state for Instagram external echo messages (#13700)

Instagram external echo messages were being saved with status:
delivered, but the message meta UI did not treat Instagram as a channel
eligible for delivered-state rendering. As a result, these messages fell
back to progress and showed as “Sending”. This change updates the
message status mapping in the new message UI to include Instagram in the
delivered-state condition.

app/javascript/dashboard/components-next/message/MessageMeta.vue

@@ -81,6 +81,7 @@ const isDelivered = computed(() => {
     isATwilioChannel.value ||
     isASmsInbox.value ||
     isAFacebookInbox.value ||
+    isAnInstagramChannel.value ||
     isATiktokChannel.value
   ) {
     return sourceId.value && status.value === MESSAGE_STATUS.DELIVERED;