fix(conversations): filter canal='turnero' out of individual chat message views

get_user_messages.php and get_recent_messages.php now exclude canal='turnero'
so the main bot chat only shows bot messages even for users who also have
turnero conversations.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/get_recent_messages.php

@@ -27,7 +27,7 @@ try {
             u.name
          FROM conversations c
          JOIN users u ON c.user_id = u.id
-         WHERE c.content IS NOT NULL AND c.content != ''
+         WHERE c.content IS NOT NULL AND c.content != '' AND (c.canal IS NULL OR c.canal = 'bot')
          ORDER BY c.created_at DESC
          LIMIT 10"
     );