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/App.svelte

@@ -7,14 +7,20 @@
 
   let route = $state("/");
   let gameId = $state(null);
+  let filterGenre = $state("");
+  let filterYear = $state("");
 
   function parseHash() {
     const hash = window.location.hash.slice(1) || "/";
-    const [pathPart] = hash.split("?"); // strip query params
+    const [pathPart, qs] = hash.split("?");
     const parts = pathPart.split("/").filter(Boolean);
     if (parts.length === 0 || (parts.length === 1 && parts[0] === "")) {
       route = "/";
       gameId = null;
+      // Parse filter query params
+      const params = new URLSearchParams(qs || "");
+      filterGenre = params.get("genre") || "";
+      filterYear = params.get("year") || "";
     } else if (parts[0] === "game" && parts[1]) {
       route = "/game";
       gameId = parts[1];
@@ -40,7 +46,7 @@
 
 <main class="container">
   {#if route === "/"}
-    <Library />
+    <Library genreFilter={filterGenre} yearFilter={filterYear} />
   {:else if route === "/game" && gameId}
     <GameDetail id={gameId} />
   {:else if route === "/play" && gameId}