With "number=no" the current section is no longer written to the utility
file and there is no way to get it in the toc. What you can do is
to enable section numbering but remove it from the output.
\setuphead
[chapter]
[numbercommand=\gobbleoneargument,
distance=0pt]
Great ! With \setuphead[alternative=middle] there's still an empty/blank
space above the chapter head though (where the chapter number is located
when leaving out the numbercommand)...
\setuphead[chapter][%
alternative=middle,
number=yes,
numbercommand=\gobbleoneargument,
distance=0pt]