feat(admin): ask the panel to restart, from verdande's own settings

A container cannot replace its own image from the inside, so "update" is really
"ask whoever owns the container to recreate it" — Yggdrasil pulls `:latest` on the
way, which is what makes a restart an update at all. This removes the second
browser tab, not the panel's authority: the panel still does the work and still
records who asked.

Three settings, needed together, and the page names whichever are missing — an
operator reading "not configured" should not have to go and find out which of
three. The token is never sent to a browser; the page is told only whether it is
set.

Answers 202 rather than waiting. The panel stops this container as part of
answering, so the reply may never arrive, and a request cut off mid-flight is the
successful case wearing a failure's clothes. The interface believes neither answer
and polls /healthz until it responds.

Administrators only, and sessions only. A leaked API token that could restart the
server is a denial of service in one request.

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

web/src/lib/api.js

@@ -199,6 +199,8 @@ export const api = {
 	deleteUser: (id) => del(`/users/${id}`),
 	revokeInvite: (id) => del(`/invites/${id}`),
 	listErrors: () => get('/errors'),
+	panelStatus: () => get('/panel'),
+	restartFromPanel: () => post('/panel/restart'),
 
 	// The nightly backup, which ran since the beginning with nothing to show it.
 	// The OAuth client itself, which is the instance's registration with Google