refactor(frontend): migrate state management to jotai and jotai-tanstack-query

Replace React Context + manual useEffect data fetching with jotai atoms
for state management and jotai-tanstack-query for server state caching.

- Add jotai, jotai-tanstack-query, @tanstack/query-core dependencies
- Create atoms for auth (primitive + action), feeds (suspense query),
  and articles (infinite query with cursor-based pagination)
- Wire up Provider, HydrateQueryClient, and StoreInitializer in main.tsx
- Migrate all components from useAuth() context to jotai atoms
- Replace manual fetch logic in FeedSidebar/FeedList with feedsAtom
- Replace usePaginatedArticles hook with articlesInfiniteAtom
- Add queryClient.invalidateQueries() after mutations for automatic
  cache refresh
- Add ErrorBoundary and LoadingSpinner components for Suspense support
- Remove callback prop chains (onFeedAdded, onFeedChanged, etc.)
  in favor of query invalidation

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

1 files changed, 4 insertions, 2 deletions

diff --git a/frontend/src/components/ProtectedRoute.tsx b/frontend/src/components/ProtectedRoute.tsx
index e03a4f0..8dd191c 100644
--- a/frontend/src/components/ProtectedRoute.tsx
+++ b/frontend/src/components/ProtectedRoute.tsx
@@ -1,13 +1,15 @@
+import { useAtomValue } from "jotai";
 import type { ReactNode } from "react";
 import { Redirect } from "wouter";
-import { useAuth } from "../contexts/AuthContext";
+import { authLoadingAtom, isLoggedInAtom } from "../atoms";
 
 interface Props {
 	children: ReactNode;
 }
 
 export function ProtectedRoute({ children }: Props) {
-	const { isLoggedIn, isLoading } = useAuth();
+	const isLoggedIn = useAtomValue(isLoggedInAtom);
+	const isLoading = useAtomValue(authLoadingAtom);
 
 	if (isLoading) {
 		return (