Build a todo app with filters and persistence

• Add a todo with Enter or the button; empty or whitespace-only input is rejected
• Toggle done with a checkbox; edit text inline by double-click (Enter saves, Escape cancels, empty text deletes the todo); delete with a button
• Filters All, Active and Completed, with the current filter reflected in the URL hash (#/active)
• Shows the count of items left ("1 item left", "3 items left") and a Clear completed button that appears only when there are completed items
• A toggle-all control marks everything done, or everything active if all are done
• Todos and the filter survive a page reload using localStorage, tolerating missing or corrupted stored data
• Empty states for no todos and for an empty filter result

Only after every requirement works.

• Drag to reorder todos
• Undo the last delete or clear action
• Sync across browser tabs with the storage event