feat(dashboard): show "Updating to a new version..." on loader during version-hash reload

When the dashboard reloads because the build version hash changed, surface that
on the loading screen instead of the generic "Initializing dashboard..." so the
user understands why they bounced.

Carry the signal across the hard reload via a sessionStorage flag set in
versionCheck just before reloadOnce(), and consume-and-clear it once on the
loader's first render.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/DashboardLoader.css

@@ -43,6 +43,11 @@
   color: var(--text-secondary);
 }
 
+.dashboard-loader__message--update {
+  color: var(--accent, var(--text));
+  font-weight: 500;
+}
+
 .dashboard-loader__steps {
   display: flex;
   flex-direction: column;