feat(client): initialize React + Vite frontend foundation

Set up the client-side React application with Vite bundler:
- Add React 19 and Vite 7 with the React plugin
- Create index.html entry point and App component
- Configure Vite with API proxy to backend server
- Add client build scripts to package.json
- Update tsconfig for React JSX and DOM types
- Fix TypeScript errors in auth code (JWT_SECRET type narrowing)

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

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

1 files changed, 8 insertions, 0 deletions

diff --git a/src/client/App.tsx b/src/client/App.tsx
new file mode 100644
index 0000000..fa42302
--- /dev/null
+++ b/src/client/App.tsx
@@ -0,0 +1,8 @@
+export function App() {
+	return (
+		<div>
+			<h1>Kioku</h1>
+			<p>Spaced repetition learning app</p>
+		</div>
+	);
+}