Add Settings -> Database viewer (Adminer) for local devs and any admin

Local dev gets an unauthenticated Adminer instance bound to loopback
only. In production, any account with is_admin=true can open it -
the app mints a short-lived token from a live admin session, which
Nginx's new db.ciagent.org block exchanges for a session cookie that
re-checks admin status on every request, instead of a shared static
password that wouldn't scale to multiple admins or revoke live.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

apps/web/hooks/use-auth.ts

@@ -47,6 +47,12 @@ export function useSetSystemSecret() {
   });
 }
 
+export function useCreateDbViewerSession() {
+  return useMutation({
+    mutationFn: () => api.createDbViewerSession(),
+  });
+}
+
 export function useSystemLogs() {
   return useQuery({
     queryKey: ["system-logs"],