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>

peptide-news-plugin.php

@@ -3,7 +3,7 @@
  * Plugin Name:       Peptide News Aggregator
  * Plugin URI:        https://github.com/peptiderepo/peptide-news-plugin
  * Description:       Aggregates and displays the latest peptide research news from multiple sources with click analytics and trend reporting.
- * Version:           1.2.2
+ * Version:           1.3.0
  * Author:            Peptide News Team
  * Author URI:        https://github.com/peptiderepo
  * License:           GPL-2.0+
@@ -22,7 +22,7 @@ if ( ! defined( 'WPINC' ) ) {
 /**
  * Current plugin version — follows SemVer.
  */
-define( 'PEPTIDE_NEWS_VERSION', '1.2.2' );
+define( 'PEPTIDE_NEWS_VERSION', '1.3.0' );
 define( 'PEPTIDE_NEWS_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 define( 'PEPTIDE_NEWS_PLUGIN_URL', plugin_dir_url( __FILE__ ) );
 define( 'PEPTIDE_NEWS_PLUGIN_BASENAME', plugin_basename( __FILE__ ) );