A multipart POST to the plugin API hangs and never completes on this host: no
status code, and no server-side trace of any kind. The correlation was exact —
every page using URLSearchParams worked, every page using FormData hung, which
is why scheduler and partnership appeared fine while docker, rsync, settings,
auth, arrs, fallback and monitor did not. URLSearchParams has the same append
API and fetch sets the urlencoded content type for it, so each site is a
one-token change with the payload logic untouched.
Documents each tab's purpose, what it renders, and which endpoints it polls.
Pages that start with markup get the header in a <?php ?> block so it never
reaches the browser.
Also corrects the layer diagram in README-unraid.md: eight of eleven pages hold
no PHP logic and poll api/ for everything — only auth, monitor and scheduler
require an include/ file directly.