fix(webapp): drop the stray full stop from the Dark system setting row

It was the only settings row description on the account page ending in one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: samejr

apps/webapp/app/routes/account._index/route.tsx

@@ -723,7 +723,7 @@ export default function Page() {
                       <div className={cn("flex-1", SETTINGS_ROW_TITLE_GAP)}>
                         <Label>Dark</Label>
                         <SettingsRowDescription>
-                          Choose the theme for the dark system setting.
+                          Choose the theme for the dark system setting
                         </SettingsRowDescription>
                       </div>
                       <div className="flex flex-none items-center">