Measured chain from live preview showed the cap on .cm-content at 700px,
while .cm-sizer - the element closest() matched first - is already
uncapped at 1680px. The class-name shortcut therefore locked onto the
wrong element and returned before the fallback walk could find the real
one, so the cap survived and the container query correctly collapsed the
grid to one column.
widenHost now always measures computed max-width outward from the
dashboard's parent. The decision is extracted as firstCappedIndex and
tested against the real measured chains for both live preview and
reading view, so a class-name assumption cannot silently break it again.
Adds .cm-content to the CSS fallback.
