Fix React hooks order - all useState at top

src/App.tsx

@@ -19,23 +19,6 @@ import { PendingValidationView } from './components/PendingValidationView';
 export default function App() {
   const [session, setSession] = useState<AuthSession | null>(() => getStoredSession());
 
-  useEffect(() => {
-    console.log('[App] session changed:', session ? 'logged in' : 'logged out');
-  }, [session]);
-
-  const handleSignOut = () => {
-    signOut();
-    setSession(null);
-  };
-
-  if (!session) {
-    return <LoginPage onLogin={() => {
-      const stored = getStoredSession();
-      console.log('[App] onLogin, stored session:', stored ? 'found' : 'null');
-      setSession(stored);
-    }} />;
-  }
-
   const [appState, setAppState] = useState<AppState>({
     headers: [],
     data: [],
@@ -53,6 +36,23 @@ export default function App() {
   const [pendingRows, setPendingRows] = useState<Record<string, { rowIndex: number; originalData: ExcelRow; newData: ExcelRow; articleName: string }>>({});
   const [isSavingAll, setIsSavingAll] = useState(false);
 
+  useEffect(() => {
+    console.log('[App] session changed:', session ? 'logged in' : 'logged out');
+  }, [session]);
+
+  const handleSignOut = () => {
+    signOut();
+    setSession(null);
+  };
+
+  if (!session) {
+    return <LoginPage onLogin={() => {
+      const stored = getStoredSession();
+      console.log('[App] onLogin, stored session:', stored ? 'found' : 'null');
+      setSession(stored);
+    }} />;
+  }
+
   useEffect(() => {
     const loadDefaultData = async () => {
       // In dev: Vite proxy handles /dropbox-file (see vite.config.ts)