Checks send no Referer header, so Hetzner answers (closes #191)

The Hetzner speed-test servers close the connection without an answer
when the request has a Referer header. The browser sends one unless the
page comes with the image's Referrer-Policy: no-referrer header, which a
static host and make dev do not send. Each check now sets
referrerPolicy: "no-referrer".

Model: opus-5-5

TODO.md

@@ -23,6 +23,12 @@ Run `make frontend-viewport-test` in CI as its own step; it is not part of
 
 # Completed Steps
 
+- 2026-10-26: the six Hetzner targets answer wherever the page is served from
+  ([#191](https://git.eeqj.de/sneak/netwatch/issues/191)). They close the
+  connection without an answer when the request has a `Referer` header. The
+  browser sent one unless the page came with the image's
+  `Referrer-Policy: no-referrer` header, which a static host and `make dev` do
+  not send. Each check now sets `referrerPolicy: 'no-referrer'`
 - 2026-10-19: the server's `OnStart` hook in `internal/server/server.go` starts
   `listenAndServe` with `go func() { s.listenAndServe() }()`, as the Go style
   guide asks ([#162](https://git.eeqj.de/sneak/netwatch/issues/162)); it was