Add missing Loader class and public CSS

The Peptide_News_Loader class was referenced by class-peptide-news.php
but never committed, causing a fatal error on plugin activation.
Also adds public/css/public-style.css which is enqueued by the public
class.

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

public/css/public-style.css

@@ -0,0 +1,70 @@
+/**
+ * Peptide News Aggregator – Public Styles
+ *
+ * Styles for the front-end display of peptide news articles.
+ *
+ * @since 1.0.0
+ */
+
+/* Article grid / card layout */
+.peptide-news-container {
+    display: grid;
+    gap: 1.5rem;
+}
+
+.article-card {
+    background: #fff;
+    border: 1px solid #e0e0e0;
+    padding: 1.25rem;
+    border-radius: 6px;
+    transition: box-shadow 0.2s ease;
+}
+
+.article-card:hover {
+    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+}
+
+.article-title {
+    font-size: 1.125rem;
+    font-weight: 600;
+    color: #1a1a1a;
+    margin: 0 0 0.5rem;
+    line-height: 1.4;
+}
+
+.article-title a {
+    color: inherit;
+    text-decoration: none;
+}
+
+.article-title a:hover {
+    color: #0073aa;
+}
+
+.article-meta {
+    font-size: 0.8125rem;
+    color: #666;
+    margin-bottom: 0.75rem;
+}
+
+.article-excerpt {
+    font-size: 0.9375rem;
+    line-height: 1.6;
+    color: #444;
+}
+
+.article-source {
+    display: inline-block;
+    font-size: 0.75rem;
+    background: #f0f0f0;
+    padding: 0.2rem 0.5rem;
+    border-radius: 3px;
+    color: #555;
+}
+
+.article-thumbnail {
+    width: 100%;
+    height: auto;
+    border-radius: 4px;
+    margin-bottom: 0.75rem;
+}