-- Additive: track when the admin last read a client's conversation (Conversazioni inbox).
-- A conversation is "unread" when the latest client-authored comment created_at is
-- greater than admin_last_read_at (or admin_last_read_at IS NULL).
-- nullable — existing clients keep NULL (treated as fully unread until first open).
-- Apply to prod via SSH+docker exec BEFORE pushing schema-dependent code.
-- No drops, no truncates, no data loss.

ALTER TABLE clients ADD COLUMN IF NOT EXISTS admin_last_read_at timestamptz;
