fix: notify WebSub hub about homepage URL too

Subscribers discovering via HTML rel="self" subscribe to the
homepage topic, not the feed URL. Must notify hub for all
topic URLs so those subscriptions receive updates.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

eleventy.config.js

@@ -421,6 +421,7 @@ export default function (eleventyConfig) {
     // WebSub hub notification — notify subscribers of feed updates
     const hubUrl = "https://websubhub.com/hub";
     const feedUrls = [
+      siteUrl,
       `${siteUrl}/feed.xml`,
       `${siteUrl}/feed.json`,
     ];