fix: display featured images at full width, centered

The theme was rendering featured images at WordPress 'medium' size
(300×300 square crop) instead of the full 1200×632 original. Changed
the_post_thumbnail() from 'medium' to 'full' and added responsive CSS
that scales images to 100% content width with centered alignment.

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

style.css

@@ -583,6 +583,24 @@ nav a {
   color: var(--color-text-primary);
 }
 
+/* ---- FEATURED IMAGES ---- */
+
+.ps-featured-image {
+  width: 100%;
+  text-align: center;
+  border-radius: var(--radius-lg);
+  overflow: hidden;
+}
+
+.ps-featured-image img {
+  display: block;
+  width: 100%;
+  max-width: 100%;
+  height: auto;
+  margin: 0 auto;
+  border-radius: var(--radius-lg);
+}
+
 /* ---- BADGES & TAGS ---- */
 
 .ps-badge {

template-parts/content.php

@@ -39,8 +39,8 @@
 		<?php
 		if ( has_post_thumbnail() ) {
 			?>
-			<div style="margin-bottom: var(--spacing-lg);">
-				<?php the_post_thumbnail( 'medium' ); ?>
+			<div class="ps-featured-image" style="margin-bottom: var(--spacing-lg);">
+				<?php the_post_thumbnail( 'full' ); ?>
 			</div>
 			<?php
 		}