UI: auth banner — add re-auth hint for multi-user context

Banner now shows a second line explaining how to fix it: SSH to the
Cortex host, run `claude`, follow the login prompt, restart Cortex.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/static/app.js

@@ -919,8 +919,8 @@
                 if (!d.warning) return;
 
                 const msg = d.expired
-                    ? '✕ Claude CLI token has expired — run `claude` in a terminal to re-authenticate'
-                    : `⚠ Claude CLI token expires in ${d.hours_remaining}h — run \`claude\` in a terminal to re-authenticate`;
+                    ? '✕ Claude CLI token has expired'
+                    : `⚠ Claude CLI token expires in ${d.hours_remaining}h`;
                 authBannerMsg.textContent = msg;
                 authBanner.classList.toggle('expired', !!d.expired);
                 authBanner.classList.add('show');