add dark theme

index.html

@@ -5,6 +5,20 @@
     <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>RADIUS Admin</title>
+    <!-- Critical: paint the correct background before the app CSS loads (avoids flash). -->
+    <style>
+      html { background: oklch(1 0 0); color-scheme: light; }
+      html.dark { background: oklch(0.145 0 0); color-scheme: dark; }
+    </style>
+    <script>
+      // Apply saved (or system) theme before first paint.
+      (function () {
+        var t = localStorage.getItem('radui.theme')
+        if (t === 'dark' || (!t && matchMedia('(prefers-color-scheme: dark)').matches)) {
+          document.documentElement.classList.add('dark')
+        }
+      })()
+    </script>
   </head>
   <body>
     <div id="root"></div>