perf: parallelize WebSub notifications with 5s timeout

eleventy.config.js

@@ -2179,18 +2179,19 @@ export default function (eleventyConfig) {
     }
 
     console.log(`[websub] Notifying hub for ${feedUrls.length} URLs...`);
-    for (const feedUrl of feedUrls) {
+    await Promise.all(feedUrls.map(async (feedUrl) => {
       try {
         const res = await fetch(hubUrl, {
           method: "POST",
           headers: { "Content-Type": "application/x-www-form-urlencoded" },
           body: `hub.mode=publish&hub.url=${encodeURIComponent(feedUrl)}`,
+          signal: AbortSignal.timeout(5000),
         });
         console.log(`[websub] Notified hub for ${feedUrl}: ${res.status}`);
       } catch (err) {
         console.error(`[websub] Hub notification failed for ${feedUrl}:`, err.message);
       }
-    }
+    }));
 
     // Force garbage collection after post-build work completes.
     // V8 doesn't return freed heap pages to the OS without GC pressure.