refactor(ui): remove unused Sort button from MyDay header

It was a no-op placeholder command; removed the button, command,
locale keys, and now-unused Icon.Sort geometry.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ClaudeDo.Localization/locales/en.json

@@ -61,7 +61,6 @@
     }
   },
   "tasks": {
-    "sortTip": "Sort",
     "showCompletedTip": "Show completed",
     "listSettingsTip": "List settings",
     "addPlaceholder": "Add a task…",