webui: add light mode using existing Nord color variables

Instead of modifying individual class colors, this change introduces a light theme by reusing the existing Nord color variables.
This approach keeps the color system consistent and makes future theme adjustments easier.

webui/src/app.css

@@ -24,6 +24,31 @@
   --nord15: #b48ead;
 }
 
+@media (prefers-color-scheme: light) {
+  :root {
+    --nord0: #eceff4;
+    --nord1: #e5e9f0;
+    --nord2: #d8dee9;
+    --nord3: #c0c5ce;
+    
+    --nord4: #4c566a;
+    --nord5: #434c5e;
+    --nord6: #2e3440;
+    
+    --nord7: #8fbcbb;
+    --nord8: #5e81ac;
+    --nord9: #81a1c1;
+    --nord10: #4c566a;
+    
+    --nord11: #bf616a;
+    --nord12: #d08770;
+    --nord13: #ebcb8b;
+    --nord14: #a3be8c;
+    --nord15: #b48ead;
+  }
+}
+
+
 /* ---------- Base Layout ---------- */
 * {
   box-sizing: border-box;