chore: Migrate mailers from the worker to jobs (#12331)

Previously, email replies were handled inside workers. There was no
execution logs. This meant if emails silently failed (as reported by a
customer), we had no way to trace where the issue happened, the only
assumption was “no error = mail sent.”

By moving email handling into jobs, we now have proper execution logs
for each attempt. This makes it easier to debug delivery issues and
would have better visibility when investigating customer reports.

Fixes
https://linear.app/chatwoot/issue/CW-5538/emails-are-not-sentdelivered-to-the-contact

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

spec/mailers/conversation_reply_mailer_spec.rb

@@ -243,8 +243,8 @@ RSpec.describe ConversationReplyMailer do
         expect(mail.decoded).to include message.content
       end
 
-      it 'updates the source_id' do
-        expect(mail.message_id).to eq message.source_id
+      it 'builds messageID properly' do
+        expect(mail.message_id).to eq("conversation/#{conversation.uuid}/messages/#{message.id}@#{conversation.account.domain}")
       end
 
       context 'when message is a CSAT survey' do