-- Add danmaku_ttl setting (default 24 hours = 86400 seconds)
INSERT INTO system_settings (key, value, value_type, category, label, description, is_public)
SELECT 'danmaku_ttl', '86400', 'int', 'platform', '弹幕保留时间', '用户发送的弹幕在系统中保留的时间（秒）', true
WHERE NOT EXISTS (SELECT 1 FROM system_settings WHERE key = 'danmaku_ttl');