v10.5.0

feat: KoolbaseCollectionGrid (10.5.0)

The same collection laid out as a grid. Deliberately thin: it shares
KoolbaseCollectionController with KoolbaseCollectionList, so
stale-while-revalidate, pull-to-refresh and the loading/empty/error
slots behave identically — the two differ only in layout, and sharing
the controller is what keeps them from drifting on the hard parts.

Fixed crossAxisCount rather than responsive reflow: a caller who needs
reflow can vary it from a LayoutBuilder, and building it in would have
meant guessing at tile sizing for everyone else.

Tests are narrow on purpose — the controller's properties are already
covered by the list's tests, so re-testing them here would test the
same code twice. The query fake moves to test/support so two copies
can't drift.

README's 'for grids, drive the controller directly' is no longer true
and now documents the widget instead.