fix(author): exclude non-episode posts from podcast count on author pages

Old PowerScripting content includes ~259 announcement posts ("Up Next",
"Recording Tonight", etc.) that live in /podcast/ but have no podcast_url.
These were inflating Jonathan Walz's author page from ~327 real episodes
to 586 total items. Filter $podcasts to only pages with podcast_url set.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FNNC3yU5uCsjfcts7GGVow

Author: claude

themes/powershell-community/layouts/taxonomy/author.html

@@ -18,7 +18,8 @@ <h1 class="text-4xl lg:text-5xl font-bold mb-2">{{ .Title }}</h1>
     <div class="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
 
         {{ $articles := where .Pages "Section" "articles" }}
-        {{ $podcasts := where .Pages "Section" "podcast" }}
+        {{ $podcastAll := where .Pages "Section" "podcast" }}
+        {{ $podcasts := where $podcastAll "Params.podcast_url" "!=" nil }}
 
         <!-- Articles before podcast episodes so authored content appears first -->
         {{ $combined := $articles | append $podcasts }}