Add deixis UIWorker example

A ReplyToolMixin UIWorker that grounds in the user's text selection (the
<selection> block in the snapshot) and points back via select_text — both
directions of deictic reference.

examples/multi-worker/ui-worker/deixis/client/vite.config.js

@@ -0,0 +1,7 @@
+import { defineConfig } from "vite";
+
+export default defineConfig({
+  server: {
+    port: 5173,
+  },
+});