fix: exclude unlisted/private posts from weekly digests

OwnYourSwarm checkin posts (visibility: unlisted) were still appearing
in /digest pages. Add isListed filter to the weeklyDigests collection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

eleventy.config.js

@@ -1502,6 +1502,7 @@ export default function (eleventyConfig) {
     const allPosts = collectionApi
       .getFilteredByGlob("content/**/*.md")
       .filter(isPublished)
+      .filter(isListed)
       .filter((item) => {
         // Exclude replies
         return !(item.data.inReplyTo || item.data.in_reply_to);