fix: match spotlight to project-navi-site reference spec

Use centered positioning (left:50% + translateX(-50%)), width:150%,
height:100%, and transparent 50% gradient — exact match to the
main project-navi-site pillar.css spotlight.

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

Author: Fieldnote-Echo

index.html

@@ -51,8 +51,11 @@
     .hero::before {
       content: '';
       position: absolute;
-      top: 0; left: 0; right: 0;
-      height: 300px;
+      top: 0;
+      left: 50%;
+      transform: translateX(-50%);
+      width: 150%;
+      height: 100%;
       background: radial-gradient(ellipse at center top, rgba(126, 184, 168, 0.08) 0%, transparent 50%);
       pointer-events: none;
       z-index: -1;