Fix thumbnail scraping: use search-based URL resolution for Google News articles

Google News RSS stores encrypted article URLs that cannot be resolved
server-side (JS SPA, no HTTP redirects, encrypted base64 IDs). Replace
the failed decode/parse strategies with DuckDuckGo search-based lookup
using article title + publisher name to find actual article pages, then
scrape OG images from those pages.

- Add find_article_url_via_search() using DuckDuckGo HTML endpoint
- Add resolve_article_for_scraping() combining redirect + search fallback
- Mark failed lookups with '_no_image' sentinel to avoid repeated retries
- Backfill button resets sentinels to allow manual re-scraping
- Clean up verbose debug instrumentation from prior attempts
- Update frontend to handle '_no_image' sentinel gracefully

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

public/class-peptide-news-public.php

@@ -95,7 +95,9 @@ class Peptide_News_Public {
         ?>
         <div class="pn-news-feed pn-layout-<?php echo esc_attr( $layout ); ?>">
             <?php foreach ( $articles as $article ) :
-                $thumb = ! empty( $article->thumbnail_url ) ? $article->thumbnail_url : $fallback_thumb;
+                $thumb = ( ! empty( $article->thumbnail_url ) && '_no_image' !== $article->thumbnail_url )
+                    ? $article->thumbnail_url
+                    : $fallback_thumb;
                 $date  = wp_date( 'M j, Y', strtotime( $article->published_at ) );
             ?>
                 <article class="pn-article" data-article-id="<?php echo esc_attr( $article->id ); ?>">