feat(ui): modern shadcn/ui theme with violet accent across all pages

Add shadcn/ui (Radix + Tailwind 4) components, zinc/violet theme tokens and self-hosted Inter. New header with user menu, Steam cover art, skeletons and toasts. Replace @mdi/font with lucide-react. Fix: top-owned list on the landing page only showed with top-played entries; numbers use the app language.

src/components/GameCover.jsx

@@ -0,0 +1,30 @@
+import {useState} from 'react';
+import {Gamepad2} from 'lucide-react';
+
+import {cn} from '@/lib/utils';
+import {coverUrl} from '@/utils/games.js';
+
+/**
+ * Steam store header (460x215). Falls back to a neutral tile when the app has no header image.
+ */
+export default function GameCover({appid, className}) {
+    const [failed, setFailed] = useState(false);
+
+    return (
+        <div className={cn('aspect-[460/215] overflow-hidden rounded-md bg-muted', className)}>
+            {failed ? (
+                <div className="flex size-full items-center justify-center text-muted-foreground">
+                    <Gamepad2 className="size-1/3 max-h-8"/>
+                </div>
+            ) : (
+                <img
+                    src={coverUrl(appid)}
+                    alt=""
+                    loading="lazy"
+                    className="size-full object-cover"
+                    onError={() => setFailed(true)}
+                />
+            )}
+        </div>
+    );
+}