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, 20 insertions, 0 deletions

diff --git a/src/client/test/atomTestUtils.tsx b/src/client/test/atomTestUtils.tsx
new file mode 100644
index 0000000..9ff57e3
--- /dev/null
+++ b/src/client/test/atomTestUtils.tsx
@@ -0,0 +1,20 @@
+import type { WritableAtom } from "jotai";
+import { useHydrateAtoms } from "jotai/utils";
+import type { ReactNode } from "react";
+
+type AnyWritableAtom = WritableAtom<unknown, unknown[], unknown>;
+
+/**
+ * Component that hydrates Jotai atoms with initial values before rendering children.
+ * Use this in tests to pre-populate async atoms, bypassing Suspense.
+ */
+export function HydrateAtoms({
+	initialValues,
+	children,
+}: {
+	initialValues: Iterable<readonly [AnyWritableAtom, unknown]>;
+	children: ReactNode;
+}) {
+	useHydrateAtoms([...initialValues]);
+	return <>{children}</>;
+}