Adjust AdminPanel spacing and enhance modal UI effects

Reduced grid gap in AdminPanel for better spacing consistency. Improved modal overlay and card design with stronger darkening, added blur, and responsive adjustments to prevent layout issues in smaller viewports.

frontend/src/components/AdminPanel.jsx

@@ -124,7 +124,7 @@ export default function AdminPanel() {
               </button>
             </div>
 
-            <div style={{ marginTop: 12, display: "grid", gap: 10 }}>
+            <div style={{ marginTop: 12, display: "grid", gap: 8 }}>
               <input
                 value={displayName}
                 onChange={(e) => setDisplayName(e.target.value)}