fix(setup): print the hub's public URL, not the host the reader typed

The setup pages build commands that get pasted into a terminal on a *different*
machine, but they built them from location.origin. Open the console by LAN IP or
over a tunnel and the enrolment one-liner told the target machine to curl an
address it may not resolve at all.

/docs and /enroll/:token are now served through a template that stamps in
config.baseUrl — PUBLIC_URL where set, the proxied request host otherwise — with
location.origin left as a fallback for the unsubstituted file. The remaining
127.0.0.1 references are the loopback VNC port on the machine being registered,
which is meant to be literal.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

server/index.js

@@ -120,9 +120,25 @@ app.get('/install.ps1', serveInstallScript('install.ps1', 'text/plain; charset=u
 app.use('/novnc', express.static(NOVNC_DIR, { maxAge: '7d', immutable: true }));
 app.use(express.static(PUBLIC_DIR));
 
+// The setup pages print commands that get run on *another* machine, so they must
+// name this hub's public address — not whatever host the reader happens to have
+// typed. Reached over the LAN IP, `location.origin` would hand out a URL the
+// target machine may not be able to resolve at all.
+function sendPageWithHub(file) {
+  return (req, res) => {
+    let html;
+    try {
+      html = fs.readFileSync(path.join(PUBLIC_DIR, file), 'utf8');
+    } catch {
+      return res.status(500).type('text/plain').send(`${file} missing from this deployment`);
+    }
+    res.type('html').send(html.split('__HUB__').join(config.baseUrl(req)));
+  };
+}
+
 app.get('/viewer', (_req, res) => res.sendFile(path.join(PUBLIC_DIR, 'viewer.html')));
-app.get('/docs', (_req, res) => res.sendFile(path.join(PUBLIC_DIR, 'docs.html')));
-app.get('/enroll/:token', (_req, res) => res.sendFile(path.join(PUBLIC_DIR, 'enroll.html')));
+app.get('/docs', sendPageWithHub('docs.html'));
+app.get('/enroll/:token', sendPageWithHub('enroll.html'));
 app.get('/s/:token', (_req, res) => res.sendFile(path.join(PUBLIC_DIR, 'share.html')));
 
 app.use((req, res) => {