Replace canvas::page, canvas::text and DateField with onestore::page; the
inherent layout methods on Outline and Title become the Arrange trait and
outline_layout, and parley affinities map through canvas::affinity. The
branch-carried Layout.reserved_width and Format.list_spacing fields are
ported to onestore in the rebased base commit.

Validation: canvas 95 tests, snowbound 29 tests, workspace Clippy with
warnings denied, fuzz canvas-editor target, and target/Snowbound.app built
with its icon.

Assisted-by: claude-fable-5.1