fix: Add z-index to navbar to sit above radar grid overlay

Dashboard pages have a .radar-bg element with a grid pattern that
was showing through the navbar. Adding position: relative and z-index: 10
ensures the nav appears above the background effects.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/css/core/layout.css

@@ -592,6 +592,8 @@
     background: #151a23 !important; /* Explicit color - forced to ensure consistency */
     border-bottom: 1px solid var(--border-color);
     padding: 0 20px;
+    position: relative;
+    z-index: 10;
 }
 
 @media (min-width: 1024px) {

static/css/index.css

@@ -643,6 +643,8 @@ header h1 {
     background: #151a23 !important; /* Explicit color - forced to ensure consistency */
     border-bottom: 1px solid var(--border-color);
     padding: 0 20px;
+    position: relative;
+    z-index: 10;
 }
 
 @media (min-width: 1024px) {