Add router base path for GitHub Pages

Configure SolidJS Router with base path in production to correctly
match routes when deployed to /gc-solid-ui/. This fixes the landing
page not rendering issue.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: binnodon

src/app.tsx

@@ -6,8 +6,10 @@ import { SolidBaseRoot } from "@kobalte/solidbase/client"
 import "~/styles/globals.css"
 
 export default function App() {
+  const base = import.meta.env.PROD ? "/gc-solid-ui" : ""
+
   return (
-    <Router root={SolidBaseRoot}>
+    <Router base={base} root={SolidBaseRoot}>
       <FileRoutes />
     </Router>
   )