MapControlMenu's 'fit inside the map' height clamp is right for a map
host but wrong for ShareButton's header fallback: the fallback tags
the ~56px header band as the area (data-map-area='share-fallback'),
and the menu clamped INSIDE it -- measured on upg-100-mfe, a 291px
share menu rendered with a 69px scrolling body. A menu must never
outgrow a MAP's walls, but a header band is not a wall (nothing clips
below it), so a share-fallback area now bounds against the VIEWPORT.
Measured: header host body 291/291 no scroll, menu 342px tall below
the band; map host (doxa-simple-map) unchanged, 287/287 within the
map. Real map areas keep the original walls -- only the self-tagged
fallback takes the new branch.