Restructure layout: search in sidebar, upload in header

- Removed toolbar (Library title, search, upload button) from library
- Moved search box into the sidebar alongside Year/Genre filters
- Removed 'Filters' heading from sidebar
- Replaced 'Library' nav button in header with '+ Upload' button
- Genre filters now sorted by count (desc) instead of alphabetically
- Cleaned up unused CSS

frontend/src/App.svelte

@@ -9,6 +9,7 @@
   let gameId = $state(null);
   let filterGenre = $state("");
   let filterYear = $state("");
+  let uploadTriggered = $state(0);
 
   function parseHash() {
     const hash = window.location.hash.slice(1) || "/";
@@ -42,11 +43,11 @@
   });
 </script>
 
-<Header />
+<Header onUploadClick={() => uploadTriggered++} />
 
 <main class="container">
   {#if route === "/"}
-    <Library genreFilter={filterGenre} yearFilter={filterYear} />
+    <Library genreFilter={filterGenre} yearFilter={filterYear} {uploadTriggered} />
   {:else if route === "/game" && gameId}
     <GameDetail id={gameId} />
   {:else if route === "/play" && gameId}