Store and serde derives coexist on all 23 dashboard types (prototype
confirmed). Settings carries the saved-format version (1) as the
migration hook anchor; Dashboard::blank() is the post-Clear empty
campaign. mock() now builds Settings via Default.
Remove unused imports (nav, sidebar, state, mock, inventory, item,
numput), the unused qty closure, the unused #![feature] gate, and a
module-scoped allow(dead_code) for the unmounted search stubs.
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.
