refactor: reduce theme selector width for compact display

Changed theme selector from w-48 (192px) to w-32 (128px) since
theme names are short (Dark, Light, Plan9). More compact and
better proportioned for the content.

src/components/SettingsViewer.tsx

@@ -54,7 +54,7 @@ export function SettingsViewer() {
                   </p>
                 </div>
                 <Select value={themeId} onValueChange={setTheme}>
-                  <SelectTrigger id="theme" className="w-48">
+                  <SelectTrigger id="theme" className="w-32">
                     <SelectValue />
                   </SelectTrigger>
                   <SelectContent>