Refactor frontend to hook-based architecture

Extract logic from god components into custom hooks (useAuthCheck,
useConversations, useChat, usePresignedUrl, useAdminUsers, useOIDCAuth).
Eliminate unnecessary useEffects per React guidelines — scroll is now
imperative, isAdmin comes from useAuthCheck instead of a separate fetch.
ConversationList becomes a pure presentational component. Wrap bubble
components in React.memo.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

raggr-frontend/src/App.tsx

@@ -1,48 +1,13 @@
-import { useState, useEffect } from "react";
-
 import "./App.css";
 import { AuthProvider } from "./contexts/AuthContext";
 import { ChatScreen } from "./components/ChatScreen";
 import { LoginScreen } from "./components/LoginScreen";
-import { conversationService } from "./api/conversationService";
+import { useAuthCheck } from "./hooks/useAuthCheck";
 import catIcon from "./assets/cat.png";
 
 const AppContainer = () => {
-  const [isAuthenticated, setAuthenticated] = useState<boolean>(false);
-  const [isChecking, setIsChecking] = useState<boolean>(true);
+  const { isAuthenticated, isChecking, isAdmin, setAuthenticated } = useAuthCheck();
 
-  useEffect(() => {
-    const checkAuth = async () => {
-      const accessToken = localStorage.getItem("access_token");
-      const refreshToken = localStorage.getItem("refresh_token");
-
-      // No tokens at all, not authenticated
-      if (!accessToken && !refreshToken) {
-        setIsChecking(false);
-        setAuthenticated(false);
-        return;
-      }
-
-      // Try to verify token by making a request
-      try {
-        await conversationService.getAllConversations();
-        // If successful, user is authenticated
-        setAuthenticated(true);
-      } catch (error) {
-        // Token is invalid or expired
-        console.error("Authentication check failed:", error);
-        localStorage.removeItem("access_token");
-        localStorage.removeItem("refresh_token");
-        setAuthenticated(false);
-      } finally {
-        setIsChecking(false);
-      }
-    };
-
-    checkAuth();
-  }, []);
-
-  // Show loading state while checking authentication
   if (isChecking) {
     return (
       <div className="h-screen flex flex-col items-center justify-center bg-cream gap-4">
@@ -61,7 +26,7 @@ const AppContainer = () => {
   return (
     <>
       {isAuthenticated ? (
-        <ChatScreen setAuthenticated={setAuthenticated} />
+        <ChatScreen setAuthenticated={setAuthenticated} isAdmin={isAdmin} />
       ) : (
         <LoginScreen setAuthenticated={setAuthenticated} />
       )}