refactor: remove redundant fallback and legacy handling on drawing load failure

This commit simplifies `loadDrawing` in `useDrawingSession.ts` by removing silent fallbacks that were fetching the drawing list and redirecting users or auto-creating drawings when loading a specific drawing failed. Instead, the error state is simply set, ensuring errors surface cleanly.

src/client/main.tsx

@@ -0,0 +1,16 @@
+import { StrictMode } from "react";
+import { createRoot } from "react-dom/client";
+import { App } from "./App";
+import "./styles.css";
+
+const root = document.getElementById("root");
+
+if (!root) {
+  throw new Error("Root element not found");
+}
+
+createRoot(root).render(
+  <StrictMode>
+    <App />
+  </StrictMode>,
+);