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

webui/src/lib/bootstrap.ts

@@ -0,0 +1,40 @@
+import type { BootstrapResponse } from "./types";
+
+/**
+ * Fetch a short-lived token + the WebSocket path from the gateway's
+ * ``/webui/bootstrap`` endpoint. Localhost-only on the server side.
+ */
+export async function fetchBootstrap(
+  baseUrl: string = "",
+): Promise<BootstrapResponse> {
+  const res = await fetch(`${baseUrl}/webui/bootstrap`, {
+    method: "GET",
+    credentials: "same-origin",
+  });
+  if (!res.ok) {
+    throw new Error(`bootstrap failed: HTTP ${res.status}`);
+  }
+  const body = (await res.json()) as BootstrapResponse;
+  if (!body.token || !body.ws_path) {
+    throw new Error("bootstrap response missing token or ws_path");
+  }
+  return body;
+}
+
+/** Derive a WebSocket URL from the current window location and the server-provided path.
+ *
+ * Keeps the path segment exactly as the server registered it: the root ``/``
+ * stays ``/`` and non-root paths are not given an extra trailing slash. This
+ * matters because some WS servers dispatch handshakes based on the literal
+ * path, not a normalised form.
+ */
+export function deriveWsUrl(wsPath: string, token: string): string {
+  const path = wsPath && wsPath.startsWith("/") ? wsPath : `/${wsPath || ""}`;
+  const query = `?token=${encodeURIComponent(token)}`;
+  if (typeof window === "undefined") {
+    return `ws://127.0.0.1:8765${path}${query}`;
+  }
+  const scheme = window.location.protocol === "https:" ? "wss" : "ws";
+  const host = window.location.host;
+  return `${scheme}://${host}${path}${query}`;
+}