fix(shell): resolve savedTabs undefined ReferenceError in activeTab init

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/src/components/Shell.jsx

@@ -271,9 +271,13 @@ export default function Shell({ api }) {
     ]
   })
   const [activeTab, setActiveTab] = useState(() => {
-    if (savedTabs) {
-      return savedTabs[0]?.id || 1
+    try {
+      const raw = localStorage.getItem(TABS_STORAGE_KEY)
+      if (raw) {
+        const parsed = JSON.parse(raw)
+        if (Array.isArray(parsed) && parsed.length > 0) return parsed[0]?.id || 1
       }
+    } catch {}
     return 1
   })
   const activeTabRef = useRef(activeTab)