feat: add favicon and logo assets, update App component to use logo

webapp/src/App.tsx

@@ -672,7 +672,7 @@ export default function App() {
         <div className="app-shell">
           <header className="topbar">
             <div className="brand">
-              <Shield size={20} className="brand-icon" />
+              <img src="/logo-64.png" alt="NodeWarden logo" className="brand-logo" />
               <span>NodeWarden</span>
             </div>
             <div className="topbar-actions">

webapp/src/styles.css

@@ -235,14 +235,15 @@ body,
 .brand {
   display: inline-flex;
   align-items: center;
-  gap: 10px;
   font-size: 34px;
   font-weight: 800;
   color: #1e293b;
 }
 
-.brand-icon {
-  color: #334155;
+.brand-logo {
+  width: 57px;
+  height: 57px;
+  object-fit: contain;
 }
 
 .topbar-actions {