Drag the handle (or focus it and use the arrow keys). The weeks are a plain wrapping CSS grid
that re-flows instantly; every day square is anchored to its invisible cell with
data-⚓️-fill + data-⚓️-transition="glide" and slides to its new band.
Month labels ride data-⚓️-side="above" their first week, the handle sits
data-⚓️-side="after" the frame, and the tooltip glides between days because
hovering just moves the --hot anchor name (near the right edge
data-⚓️-try="flip-x" flips it to end-align). JS only builds the data and tracks the pointer.