Replaces the two-row, mixed-control filter UI under the search bar with a
single segmented row for scope (All/People/Notes) and a Tune icon button
that opens a ModalBottomSheet containing Source, Follows-only, and Sort
controls. A primary-color dot on the icon indicates non-default filter
state.
Also renames SearchSortOrder.DEFAULT_EVENT/DEFAULT_PEOPLE to
EVENT_DEFAULT/PEOPLE_DEFAULT for consistency with EVENT_OPTIONS/
PEOPLE_OPTIONS, and routes the sheet's reset button through these
canonical constants so the UI default cannot drift from the ViewModel.
davotoula
458d9bcbab