Save downloads dashboard.json, Load opens a file picker and imports
through apply_import with errors reported in the modal, Clear asks for
confirmation then wipes to Dashboard::blank(). App provides the store
and ModalState and mounts the modal; init_hydrated starts autosave.
Doc comments on all modules, components, entities, helpers and type
aliases; larger comments on the important entities (Dashboard, PlayerData,
Context, App, Numput, item data). No behavior changes.
