fix: match homepage WebSub topic URL with trailing slash

The HTML self link produces https://rmendes.net/ (with slash)
but hub was notified with https://rmendes.net (no slash).
Hub treats these as different topics.

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

eleventy.config.js

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