V157: Widen phoenix_kit_annotations_kind_check for the new "image" kind.

PR #660 exposed Etcher 0.9's :image tool in the media viewer's toolbar (media_canvas_viewer.html.heex) without widening the CHECK constraint (or the schema's @kinds) to match — the same regression V130's moduledoc warns about for "marker". Without this, inserting an image annotation is rejected by the DB and silently fails to persist across a reload.

Idempotent: each ADD CONSTRAINT is preceded by DROP CONSTRAINT IF EXISTS on the same prefixed table.