feat: Add attachment support for Signal and WhatsApp channels

- Signal: Use base64Attachments field in signal-cli-rest-api
- WhatsApp: Implement Baileys attachment sending for images, videos, audio, and documents
- Both channels retrieve attachments from Zammad Store model
- Support multiple attachments per message

packages/zammad-addon-bridge/src/lib/cdr_signal.rb

@@ -334,6 +334,20 @@ class CdrSignal
     options = {}
     options[:conversationId] = ticket.number if ticket
 
+    # Get attachments from the article
+    attachments = Store.list(object: 'Ticket::Article', o_id: article.id)
+    if attachments.any?
+      attachment_data = attachments.map do |attachment|
+        {
+          data: Base64.strict_encode64(attachment.content),
+          filename: attachment.filename,
+          mime_type: attachment.preferences['Mime-Type'] || attachment.preferences['Content-Type'] || 'application/octet-stream'
+        }
+      end
+      options[:attachments] = attachment_data
+      Rails.logger.debug { "Sending #{attachment_data.length} attachment(s) with message" }
+    end
+
     @api.send_message(recipient, article[:body], options)
   end
 end