fix: resolve mermaid elk diagram error, upgrade high-res appicon and complete rebranding to G-Launcher/GaCy

frontend/index.html

@@ -5,7 +5,7 @@
     <meta charset="UTF-8" />
     <link rel="icon" type="image/svg+xml" href="/appicon.png" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <title>Firefly Launcher</title>
+    <title>G-Launcher</title>
 </head>
 
 <body>