Show the honest remaining seats for product 17 (Bootcamp Q1-2027) on all
three bootcamp pages, in the page's own language, from the availability
webhook. Progressive enhancement (static/bootcamp-availability.js): empty
and hidden by default, filled on a successful fetch; on qty 0 the cohort is
reported full, the next cohort is pointed at, and the Buy buttons are
disabled; on any timeout/error/unexpected payload the page is left exactly
as-is and the Buy buttons stay enabled. The count is never written into the
HTML as a fixed string.
