fix: auto-retry version fetch + add uptime/kill to exec allowlist

Layout.tsx: when versionError is true, automatically retry fetchVersion
after 5 s. This handles the case where the initial fetch runs during
the service-restart window after an upgrade (server not yet up), which
caused the sidebar footer to permanently show 'Version unavailable'
even though the server came back online shortly after.

exec.ts: add 'uptime' and 'kill' to ALLOWED_COMMANDS. 'uptime' was
missing, causing exec('uptime', ['-p']) in GET /api/nixserver/system/info
to throw 'Command not allowed', which rejected the entire Promise.all
and returned 500 — leaving Hostname and OS as '...' on the dashboard.

nixserver/src/components/Layout.tsx

@@ -475,8 +475,16 @@ export default function Layout() {
     }
   }, [])
 
+  // Initial fetch
   useEffect(() => { fetchVersion() }, [fetchVersion])
 
+  // Auto-retry every 5 s while in error state (handles the service-restart window after an upgrade)
+  useEffect(() => {
+    if (!versionError) return
+    const t = setTimeout(fetchVersion, 5_000)
+    return () => clearTimeout(t)
+  }, [versionError, fetchVersion])
+
   const handleUpgrade = async () => {
     if (upgradeState === 'confirm') {
       setUpgradeState('running')

server/src/core/exec.ts

@@ -24,7 +24,7 @@ const ALLOWED_COMMANDS = new Set([
   // Network
   'ss', 'ip', 'hostname',
   // System
-  'uname', 'free', 'ps',
+  'uname', 'uptime', 'free', 'ps', 'kill',
   // PHP
   'php8.2', 'php8.3',
   // Fail2ban