feat(ui): add smallest-first size sort

The redesign only offered a largest-first size sort. Keep the existing `size`
preference value as largest for compatibility with saved settings and add a new
ascending size key for users who want to find small downloads first.

The sort menu now exposes both size directions and the sorter handles the new
smallest-first option directly.

Test Plan:
- git diff --check

Refs: user redesign nitpick about Size (smallest) sort

crates/lanspread-tauri-deno-ts/src/components/topbar/SortMenu.tsx

@@ -6,6 +6,7 @@ import { GameSort } from '../../lib/types';
 const OPTIONS: ReadonlyArray<{ key: GameSort; label: string }> = [
     { key: 'az', label: 'Name (A–Z)' },
     { key: 'size', label: 'Size (largest)' },
+    { key: 'sizeAsc', label: 'Size (smallest)' },
     { key: 'status', label: 'Status' },
 ];