Library filters sidebar, clickable tags, remove Ready badge

- GameCard: removed 'Ready' badge from covers (keep '🪟 Win' for
  Windows games only — it's informative since they can't be played)
- Library: sidebar with Year + Genre checkbox filter groups
  - Each shows up to 5 items with game counts, 'Show all' button
  - Active filters shown as removable chips above the grid
  - Reset button clears all filters
  - Filters reflected in URL hash (#/?genre=FPS&year=1996)
- GameDetail: year and genre tags are now clickable links to
  #/?year=1996 or #/?genre=FPS, which opens the Library with that
  filter pre-applied
- App.svelte: parses query params from hash and passes to Library

frontend/src/lib/GameCard.svelte

@@ -28,14 +28,8 @@
       <span class="genre">{game.genre}</span>
     {/if}
   </div>
-  {#if game.ready}
-    <div class="badge" class:badge-windows={game.platform === 'windows'}>
-      {#if game.platform === 'windows'}
-        🪟 Win
-      {:else}
-        Ready
-      {/if}
-    </div>
+  {#if game.platform === 'windows'}
+    <div class="badge badge-windows">🪟 Win</div>
   {/if}
 </button>