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.
