feat: Autoredirect to Excalidraw+ if special cookie is present (#5183)

Co-authored-by: David Luzar <luzar.david@gmail.com>
Co-authored-by: dwelle <luzar.david@gmail.com>

public/index.html

@@ -52,6 +52,25 @@
       content="Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them."
     />
 
+    <script>
+      // Redirect Excalidraw+ users which have auto-redirect enabled.
+      //
+      // Redirect only the bare root path, so link/room/library urls are not
+      // redirected.
+      //
+      // Putting into index.html for best performance (can't redirect on server
+      // due to location.hash checks).
+      if (
+        window.location.pathname === "/" &&
+        !window.location.hash &&
+        !window.location.search &&
+        // if its present redirect
+        document.cookie.includes("excplus-autoredirect=true")
+      ) {
+        window.location.href = "https://app.excalidraw.com";
+      }
+    </script>
+
     <link rel="shortcut icon" href="favicon.ico" type="image/x-icon" />
 
     <!-- Excalidraw version -->