refactor(client): migrate state management from React Context to Jotai

Replace AuthProvider and SyncProvider with Jotai atoms for more granular
state management and better performance. This migration:

- Creates atoms for auth, sync, decks, cards, noteTypes, and study state
- Uses atomFamily for parameterized state (e.g., cards by deckId)
- Introduces StoreInitializer component for subscription initialization
- Updates all components and pages to use useAtomValue/useSetAtom
- Updates all tests to use Jotai Provider with createStore pattern

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/client/pages/LoginPage.tsx b/src/client/pages/LoginPage.tsx
index 835c73e..0af45c6 100644
--- a/src/client/pages/LoginPage.tsx
+++ b/src/client/pages/LoginPage.tsx
@@ -1,12 +1,15 @@
 import { faSpinner } from "@fortawesome/free-solid-svg-icons";
 import { FontAwesomeIcon } from "@fortawesome/react-fontawesome";
+import { useAtomValue, useSetAtom } from "jotai";
 import { type FormEvent, useEffect, useState } from "react";
 import { useLocation } from "wouter";
-import { ApiClientError, useAuth } from "../stores";
+import { ApiClientError } from "../api/client";
+import { isAuthenticatedAtom, loginAtom } from "../atoms";
 
 export function LoginPage() {
 	const [, navigate] = useLocation();
-	const { login, isAuthenticated } = useAuth();
+	const isAuthenticated = useAtomValue(isAuthenticatedAtom);
+	const login = useSetAtom(loginAtom);
 	const [username, setUsername] = useState("");
 	const [password, setPassword] = useState("");
 	const [error, setError] = useState<string | null>(null);
@@ -26,7 +29,7 @@ export function LoginPage() {
 		setIsSubmitting(true);
 
 		try {
-			await login(username, password);
+			await login({ username, password });
 			navigate("/", { replace: true });
 		} catch (err) {
 			if (err instanceof ApiClientError) {