feat: only show Upload button on library view

Changed hideUpload condition from route==='/play' to route!=='/'
so the + Upload button only appears on the library page.

frontend/src/App.svelte

@@ -43,7 +43,7 @@
   });
 </script>
 
-<Header onUploadClick={() => uploadTriggered++} hideUpload={route === "/play"} />
+<Header onUploadClick={() => uploadTriggered++} hideUpload={route !== "/"} />
 
 <main class="container">
   {#if route === "/"}