feat(site): add the kapa.ai Ask the docs widget

.htaccess

@@ -21,3 +21,9 @@
 # "Not Found" body and the 404.html produced by `next build` is never used.
 # The status code stays 404 either way; this only replaces the body.
 ErrorDocument 404 /404.html
+
+# CSP permissions for iggy.apache.org: the kapa.ai "Ask the docs" widget and
+# the hCaptcha bot check it is configured to use. kapa.ai is approved by VP
+# Data Privacy in the ASF privacy policy:
+# https://privacy.apache.org/policies/privacy-policy-public.html#i-kapaai
+SetEnv CSP_PROJECT_DOMAINS "https://widget.kapa.ai/ https://proxy.kapa.ai/ https://kapa-widget-proxy-la7dkmplpq-uc.a.run.app/ https://metrics.kapa.ai/ https://hcaptcha.com/ https://*.hcaptcha.com/"

src/app/layout.tsx

@@ -137,6 +137,35 @@ _paq.push(['enableLinkTracking']);
 })();`}
         </Script>
         <Matomo />
+        {/*
+          kapa.ai "Ask AI" widget, through the Kapa Open Source Program. kapa.ai
+          is approved in the ASF privacy policy:
+          https://privacy.apache.org/policies/privacy-policy-public.html#i-kapaai
+          The widget script loads on every page, but no question goes to kapa
+          until the visitor accepts the consent screen, and kapa's analytics
+          cookie and fingerprinting are off. The launcher is hidden; the
+          "Ask the docs" button in the navbar opens the modal.
+        */}
+        <Script
+          id="kapa-widget"
+          src="https://widget.kapa.ai/kapa-widget.bundle.js"
+          strategy="afterInteractive"
+          data-website-id="3ddb8a09-e3b6-497a-ba43-b48a5d983815"
+          data-project-name="Apache Iggy"
+          data-modal-title="Ask the Apache Iggy docs"
+          data-modal-ask-ai-input-placeholder="How do I create a consumer group?"
+          data-project-color="#fb4800"
+          data-project-logo="https://iggy.apache.org/img/favicon.png"
+          data-color-scheme-selector=".dark"
+          data-button-hide="true"
+          data-modal-override-open-class="kapa-ask-ai"
+          data-consent-required="true"
+          data-consent-screen-disclaimer="Ask the docs is run by kapa.ai, a third-party service. Your questions are sent to kapa.ai to generate answers, and the form is protected by hCaptcha. By continuing you agree to the [kapa.ai privacy policy](https://www.kapa.ai/content/privacy-policy) and the [hCaptcha privacy policy](https://www.hcaptcha.com/privacy)."
+          data-bot-protection-mechanism="hcaptcha"
+          data-user-analytics-cookie-enabled="false"
+          data-user-analytics-fingerprint-enabled="false"
+          data-modal-disclaimer="Answers are generated by AI from the Apache Iggy docs and code, and can be wrong. Check them against the docs before relying on them."
+        />
       </body>
     </html>
   );

src/components/ask-ai-button.tsx

@@ -0,0 +1,34 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * Opens the kapa.ai "Ask the docs" modal. The widget script in the root layout is
+ * configured with data-modal-override-open-class="kapa-ask-ai" and hides its
+ * own launcher, so this button is the only way in.
+ */
+export function AskAIButton() {
+  return (
+    <button
+      type="button"
+      className="kapa-ask-ai inline-flex items-center rounded-lg border border-fd-border bg-fd-secondary/60 px-3 py-1.5 text-sm font-medium text-fd-foreground transition-colors hover:bg-fd-accent"
+    >
+      Ask the docs
+    </button>
+  );
+}

src/lib/layout.shared.tsx

@@ -21,6 +21,7 @@ import type { BaseLayoutProps } from "fumadocs-ui/layouts/shared";
 import Image from "next/image";
 import { Logo } from "@/components/logo";
 import { GitHubStars } from "@/components/github-stars";
+import { AskAIButton } from "@/components/ask-ai-button";
 import { ASFDropdown } from "@/components/asf-dropdown";
 import { ASFMobileLinks } from "@/components/asf-mobile-links";
 import {
@@ -68,6 +69,11 @@ const sharedLinks: BaseLayoutProps["links"] = [
     on: "menu",
     children: <ASFMobileLinks />,
   },
+  {
+    type: "custom",
+    secondary: true,
+    children: <AskAIButton />,
+  },
   {
     type: "custom",
     secondary: true,
@@ -122,6 +128,11 @@ export function docsOptions(): BaseLayoutProps {
         children: <CommunityDropdown />,
       },
       communityMobileMenu,
+      {
+        type: "custom",
+        secondary: true,
+        children: <AskAIButton />,
+      },
       {
         type: "custom",
         on: "nav",