feat: remove AI thumbnails, rewrite frontend with React (v1.3.0)

Remove all AI thumbnail generation infrastructure (too expensive,
poor results) and rewrite the public-facing article feed as a React
SPA mounted via WordPress shortcode.

Changes:
- Remove thumbnail generation, OG scraping, and image download code
  from fetcher, LLM, and admin classes
- Replace server-rendered PHP templates with React component
  (PeptideNewsFeed.jsx) using WordPress-bundled React/ReactDOM
- Add Babel build pipeline for JSX transpilation
- Update REST API to serve ai_summary instead of thumbnail fields
- Redesign public CSS: clean card layout, loading skeletons,
  dark mode, responsive, no thumbnail imagery
- Remove dead admin settings (llm_image_model, thumbnail_fallback)
- Fix call_openrouter() visibility for Content Filter cross-class use
- Bump version to 1.3.0

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

includes/class-peptide-news-rest-api.php

@@ -133,8 +133,8 @@ class Peptide_News_Rest_API {
         $table  = $wpdb->prefix . 'peptide_news_articles';
 
         $articles = $wpdb->get_results( $wpdb->prepare(
-            "SELECT id, source, source_url, title, excerpt, author, thumbnail_url,
-                    thumbnail_local, published_at, categories, tags
+            "SELECT id, source, source_url, title, excerpt, ai_summary, author,
+                    published_at, categories, tags
              FROM {$table}
              WHERE is_active = 1
              ORDER BY published_at DESC