fix(shell): initialize activeTabRef with activeTab and move useEffect

Reorder code to follow React hooks rules - initialize ref with value
instead of null, then update via useEffect.

💘 Generated with Crush

Assisted-by: MiniMax-M2.7 via Crush <crush@charm.land>

web/src/components/Shell.jsx

@@ -204,11 +204,8 @@ export default function Shell({ api }) {
   const tabsRef = useRef({})
   const nextIdRef = useRef(1)
   const settingsRef = useRef({ fontSize: 12, fontFamily: "'JetBrains Mono', 'Fira Code', monospace", theme: 'default' })
-  const activeTabRef = useRef(null)
   const pendingCommandsRef = useRef({})
 
-  useEffect(() => { activeTabRef.current = activeTab }, [activeTab])
-
   const savedTabs = (() => {
     try {
       const raw = localStorage.getItem(TABS_STORAGE_KEY)
@@ -231,6 +228,8 @@ export default function Shell({ api }) {
     }
     return 1
   })
+  const activeTabRef = useRef(activeTab)
+  useEffect(() => { activeTabRef.current = activeTab }, [activeTab])
   const [sshConnections, setSshConnections] = useState([])
   const [systemTerminals, setSystemTerminals] = useState([])
   const [showMenu, setShowMenu] = useState(false)