ALTER TABLE support_messages
  ADD COLUMN media_type ENUM('text','image','video','audio') NOT NULL DEFAULT 'text' AFTER sender_role,
  ADD COLUMN media_url VARCHAR(255) NULL AFTER media_type,
  ADD COLUMN media_mime VARCHAR(100) NULL AFTER media_url,
  ADD COLUMN media_size INT NULL AFTER media_mime,
  ADD COLUMN media_name VARCHAR(255) NULL AFTER media_size;