Three modal/undo fixes. (1) Fixed one-frame flash on subdivide/inset — stale in_modal bool captured before key handlers meant modal_apply skipped the start frame; now checks modal.active() directly. (2) Undo defaults to full topology snapshots instead of position-only, so topology ops (subdivide, delete, inset) actually undo correctly out of the box. (3) Subdivide smoothing modal now uses horizontal drag (right = more smooth) matching inset/scale, replacing the radial pivot-distance interaction.