-- Byte size of the generated preview variant, so the gallery response can
-- label the mobile save sheet's rows without the client HEADing every file.
-- NULL means "not measured yet" — rows predating this migration, until the
-- read path stats them once (see fillPreviewSizes in httpapi/sizes.go).
-- (No semicolons in these comments: the migration runner splits on them.)
ALTER TABLE photos_photos ADD COLUMN preview_size_bytes integer;