Fix broken search on list pages (articles, podcast)

The client-side search filter threw a TypeError on every card because
data-tags is only rendered when an article has tags, but no articles use
tags (they use categories). Reading item.dataset.tags returned undefined
and calling .includes() on it aborted the filter loop, so search did
nothing.

Default the dataset reads to empty strings so missing attributes no
longer crash the filter.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Px3dibHBwyDeWD2HMwwzoX

Author: claude

themes/powershell-community/layouts/_default/list.html

@@ -207,9 +207,9 @@ <h3 class="text-xl font-semibold text-gray-900 mb-2">No results found</h3>
         let visibleCount = 0;
 
         contentItems.forEach(item => {
-            const title = item.dataset.title;
-            const content = item.dataset.content;
-            const tags = item.dataset.tags;
+            const title = item.dataset.title || '';
+            const content = item.dataset.content || '';
+            const tags = item.dataset.tags || '';
 
             if (title.includes(searchTerm) || content.includes(searchTerm) || tags.includes(searchTerm)) {
                 item.style.display = 'block';