feat(inbox): Enable conversation continuity for social channels (#11079)

## Summary
This PR enables and surfaces **conversation workflow** for social-style
channels that should support either:
- `Create new conversations` after resolve, or
- `Reopen same conversation`

## What is included
- Adds the conversation workflow setting UI as card-based options in
Inbox Settings.
- Expands channel availability in settings to include channels like:
  - Telegram
  - TikTok
  - Instagram
  - Line
  - WhatsApp
  - Facebook
- Updates conversation selection behavior for Line incoming messages to
respect the workflow (reopen vs create-new-after-resolved).
- Updates TikTok conversation selection behavior to respect the workflow
(reopen vs create-new-after-resolved).
- Keeps email behavior unchanged (always starts a new thread).

Fixes: https://github.com/chatwoot/chatwoot/issues/8426

## Screenshot

<img width="1400" height="900" alt="pr11079-workflow-sender-clear-tight"
src="https://github.com/user-attachments/assets/9456821f-8d83-4924-8dcf-7503c811a7b1"
/>


## How To Reproduce
1. Open `Settings -> Inboxes ->
<Telegram/TikTok/Instagram/Line/Facebook/WhatsApp inbox> -> Settings`.
2. Verify **Conversation workflow** is visible with the two card
options.
3. Toggle between both options and save.
4. For Line and TikTok, verify resolved-conversation behavior follows
the selected workflow.

## Testing
- `RAILS_ENV=test bundle exec rspec
spec/builders/messages/instagram/message_builder_spec.rb:213
spec/builders/messages/instagram/message_builder_spec.rb:255
spec/builders/messages/instagram/messenger/message_builder_spec.rb:228
spec/builders/messages/instagram/messenger/message_builder_spec.rb:293
spec/services/tiktok/message_service_spec.rb`
- Result: `16 examples, 0 failures`

## Follow-up
- Migrate Website Live Chat workflow settings into this same
conversation-workflow settings model.
- Add Voice channel support for this workflow setting.

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>

app/services/tiktok/message_service.rb

@@ -23,7 +23,12 @@ class Tiktok::MessageService
   end
 
   def conversation
-    @conversation ||= contact_inbox.conversations.first || create_conversation(channel, contact_inbox, tt_conversation_id)
+    @conversation ||= if channel.inbox.lock_to_single_conversation
+                        contact_inbox.conversations.order(created_at: :desc).first
+                      else
+                        contact_inbox.conversations.where.not(status: :resolved).order(created_at: :desc).first
+                      end
+    @conversation ||= create_conversation(channel, contact_inbox, tt_conversation_id)
   end
 
   def create_message

app/services/tiktok/messaging_helpers.rb

@@ -27,7 +27,15 @@ module Tiktok::MessagingHelpers
   end
 
   def find_conversation(channel, tt_conversation_id)
-    channel.inbox.contact_inboxes.find_by(source_id: tt_conversation_id)&.conversations&.first
+    contact_inbox = channel.inbox.contact_inboxes.find_by(source_id: tt_conversation_id)
+    return if contact_inbox.blank?
+
+    if channel.inbox.lock_to_single_conversation
+      contact_inbox.conversations.order(created_at: :desc).first
+    else
+      contact_inbox.conversations.where.not(status: :resolved).order(created_at: :desc).first ||
+        contact_inbox.conversations.order(created_at: :desc).first
+    end
   end
 
   def create_conversation(channel, contact_inbox, tt_conversation_id)