Scaffold monorepo: engine, server, and web packages

npm workspaces with three TypeScript packages: @wizwar/engine (pure
game logic), @wizwar/server (Node websocket authority), @wizwar/web
(Svelte 5 + Vite client). Server handshake and client build verified.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/web/src/main.ts

@@ -0,0 +1,6 @@
+import { mount } from "svelte";
+import App from "./App.svelte";
+
+const app = mount(App, { target: document.getElementById("app")! });
+
+export default app;