fix(microsoft-shared): make email_oauth_enabled? return true for microsoft_shared

ConversationReplyMailer#email_reply guards delivery with:

  return unless smtp_config_set_or_development? || email_smtp_enabled?
                || (email_imap_enabled? && email_oauth_enabled?)

email_oauth_enabled? in the upstream helper only recognises microsoft? and
google? providers. For our new microsoft_shared provider it returns false,
so the guard fails:
  - smtp_config_set_or_development?  false (production, no SMTP_ADDRESS)
  - email_smtp_enabled?              false (we never set channel.smtp_enabled)
  - email_imap_enabled?              true  (we set imap_enabled in callback)
  - email_oauth_enabled?             false (channel.microsoft? is false)

email_reply early-returns without calling mail(). ActionMailer ends up
with no Mail::Message, deliver_now returns nil, and the next line in
Email::SendOnEmailService raises 'undefined method message_id for nil'.

Override email_oauth_enabled? in the overlay to return true for
microsoft_shared channels.

custom/app/mailers/custom/leadchat/conversation_reply_mailer_helper_extension.rb

@@ -1,4 +1,16 @@
 module Custom::Leadchat::ConversationReplyMailerHelperExtension
+  # Treat microsoft_shared channels as OAuth-enabled email channels so the
+  # email_reply mailer action's gate guard
+  #   return unless ... || (email_imap_enabled? && email_oauth_enabled?)
+  # passes for them. Without this the mailer returns early, no mail is built,
+  # deliver_now returns nil, and Email::SendOnEmailService crashes calling
+  # .message_id on nil.
+  def email_oauth_enabled?
+    return true if @channel.respond_to?(:microsoft_shared?) && @channel&.microsoft_shared?
+
+    super
+  end
+
   # Override the OAuth SMTP routing path for microsoft_shared channels. Each
   # channel's provider_config['transport'] decides which delivery method runs:
   #