Central context for the settings a template app shares instead of prop
drilling: theme, viewMode, sidebarCollapsed and the search palette, with
the ⌘K/Ctrl+K shortcut moved out of App.
- settings persist on user action only (an effect-written theme would
freeze the OS preference for users who never toggled)
- theme still boots from the <html data-theme> attribute the pre-paint
script set; viewMode mirrors to data-view-mode as the audience-preset
hook and deliberately gates nothing yet
- Topbar: viewMode segmented control, theme toggle and search now read
the context; useAppState throws outside the provider
- tests/appState.test.tsx: defaults, persistence, rehydration, garbage
storage values, ⌘K shortcut
