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/lib/Header.svelte

@@ -1,10 +1,10 @@
 <script>
-  import { push } from "./router.js";
+  let { onUploadClick = () => {} } = $props();
 </script>
 
 <header class="header">
   <div class="header-inner">
-    <a href="#/" class="logo" onclick={(e) => { e.preventDefault(); push("/"); }}>
+    <a href="#/" class="logo">
       <svg class="logo-icon" width="36" height="36" viewBox="0 0 36 36" fill="none">
         <rect x="4" y="6" width="28" height="22" rx="2" fill="#33FF33" opacity="0.15"/>
         <rect x="6" y="8" width="24" height="16" fill="#0A0A0A"/>
@@ -17,7 +17,7 @@
       <span class="logo-text">DOSTALGIA</span>
     </a>
     <nav>
-      <button class="btn" onclick={() => push("/")}>Library</button>
+      <button class="btn" onclick={onUploadClick}>+ Upload</button>
     </nav>
   </div>
 </header>