feat: Handle external echo messages from native apps (#13371)

When businesses use WhatsApp Business App (co-existence mode) or
Instagram App or TikTok alongside Chatwoot, messages sent from the
native apps were not synced properly back to Chatwoot. This left agents
with an incomplete conversation history and no visibility into responses
sent outside the dashboard. Additionally, if these echo messages did
arrive, they appeared as "Sent by: Bot" in the UI since they had no
sender, making it confusing for agents.

This PR subscribes to WhatsApp `smb_message_echoes` webhook events and
routes them through the existing service with an `outgoing_echo` flag,
mirroring how Instagram already handles echoes. On the Instagram side,
echo messages now also carry the `external_echo` content attribute and
`delivered` status.

On the frontend, messages with `externalEcho` are distinguished from bot
messages showing a "Native app" avatar and an advisory note encouraging
agents to reply from Chatwoot to maintain the service window.

<img width="1518" height="524" alt="CleanShot 2026-01-29 at 13 37 57@2x"
src="https://github.com/user-attachments/assets/5aa0b552-6382-441f-96aa-9a62ca716e4a"
/>


Fixes
https://linear.app/chatwoot/issue/CW-4204/display-messages-not-sent-from-chatwoot-in-case-of-outgoing-echo
Fixes
https://linear.app/chatwoot/issue/PLA-33/incoming-from-me-messages-from-whatsapp-business-app-are-not-falling

app/services/tiktok/message_service.rb

@@ -1,11 +1,10 @@
 class Tiktok::MessageService
   include Tiktok::MessagingHelpers
 
-  pattr_initialize [:channel!, :content!]
+  pattr_initialize [:channel!, :content!, :outgoing_echo]
 
   def perform
     if outgoing_message?
-      # Skip processing echo messages
       message = find_message(tt_conversation_id, tt_message_id)
       return if message.present?
     end
@@ -39,7 +38,7 @@ class Tiktok::MessageService
       updated_at: tt_message_time
     )
 
-    message.sender = contact_inbox.contact if incoming_message?
+    message.sender = contact_inbox.contact if incoming_message? && !outgoing_echo
     message.status = :delivered if outgoing_message?
 
     create_message_attachments(message)
@@ -91,6 +90,7 @@ class Tiktok::MessageService
     attributes = {}
     attributes[:in_reply_to_external_id] = tt_referenced_message_id if tt_referenced_message_id
     attributes[:is_unsupported] = true unless supported_message?
+    attributes[:external_echo] = true if outgoing_echo
     attributes
   end