feat(webui): add initial webui with websocket chat flow

webui/src/tests/setup.ts

@@ -0,0 +1,14 @@
+import "@testing-library/jest-dom/vitest";
+
+// happy-dom doesn't ship with ``crypto.randomUUID``; shim a tiny v4-ish helper.
+if (!("randomUUID" in globalThis.crypto)) {
+  Object.defineProperty(globalThis.crypto, "randomUUID", {
+    value: () =>
+      "xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx".replace(/[xy]/g, (c) => {
+        const r = (Math.random() * 16) | 0;
+        const v = c === "x" ? r : (r & 0x3) | 0x8;
+        return v.toString(16);
+      }),
+    configurable: true,
+  });
+}