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

webui/src/providers/ClientProvider.tsx

@@ -0,0 +1,37 @@
+import { createContext, useContext, type ReactNode } from "react";
+
+import type { NanobotClient } from "@/lib/nanobot-client";
+
+interface ClientContextValue {
+  client: NanobotClient;
+  token: string;
+  modelName: string | null;
+}
+
+const ClientContext = createContext<ClientContextValue | null>(null);
+
+export function ClientProvider({
+  client,
+  token,
+  modelName = null,
+  children,
+}: {
+  client: NanobotClient;
+  token: string;
+  modelName?: string | null;
+  children: ReactNode;
+}) {
+  return (
+    <ClientContext.Provider value={{ client, token, modelName }}>
+      {children}
+    </ClientContext.Provider>
+  );
+}
+
+export function useClient(): ClientContextValue {
+  const ctx = useContext(ClientContext);
+  if (!ctx) {
+    throw new Error("useClient must be used within a ClientProvider");
+  }
+  return ctx;
+}