Change main system image to pc_plot_3.jpg

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: atsumitanaka

links/index.html

@@ -483,7 +483,7 @@
         <!-- ===== Main System ===== -->
         <a href="https://starrydata.nims.go.jp/starrydata2/" target="_blank" class="main-system">
             <div class="main-img-wrap">
-                <img src="../images/starrydata2.png" alt="Starrydata2 Web System">
+                <img src="images/pc_plot_3.jpg" alt="Starrydata2 Web System">
             </div>
             <div class="main-info">
                 <div class="main-label">Main System</div>