fix(ui): default covers to square

Fresh launcher profiles should start with square covers when no stored UI
settings exist. Existing stored settings still pass through the normal sanitize
path and keep their selected aspect.

Test Plan:
- git diff --check

Refs: user redesign nitpick about no-config cover aspect

crates/lanspread-tauri-deno-ts/src/hooks/useSettings.ts

@@ -48,7 +48,7 @@ export const DEFAULT_SETTINGS: UISettings = {
     accent: '#3b82f6',
     bg: 'gradient',
     density: 'normal',
-    aspect: 'box',
+    aspect: 'square',
     sort: 'status',
     filter: 'local',
 };