fix: remove duplicate mastodon webmention cards client-side

Build-time Nunjucks filter only removes static webmentions. Client-side
webmention fetcher (webmentions.js) adds NEW cards after page load, bypassing
the filter. After mastodon replies load, remove any li[data-author-url] cards
whose author URL matches a mastodon reply — keeing the richer Alpine card.

js/social-threads.js

@@ -97,6 +97,13 @@ document.addEventListener("alpine:init", () => {
           published: s.created_at,
           favourites: s.favourites_count || 0,
         }));
+
+        // Remove webmention cards (build-time or client-fetched) that duplicate mastodon replies.
+        // Webmention cards have data-author-url; Alpine x-for cards do not.
+        const mastodonAuthorUrls = new Set(this.mastodonReplies.map((r) => r.author.url));
+        document.querySelectorAll(".webmention-replies li[data-author-url]").forEach((li) => {
+          if (mastodonAuthorUrls.has(li.dataset.authorUrl)) li.remove();
+        });
       } catch {
         // fail silently
       }