Add a new Task Categories Feature (Day 1-2)

- add a Category filter dropdown in add tasks
- Category statistics like personal, home, shopping, regular
- Update task schema
- Add category selector in task form with styling

Start by locating the task schema and the add-task form entry point. Review how task statistics are currently calculated, then add the category selector, filter, statistics, schema changes, and styling described in the issue. Done means categories can be selected and filtered, and the category statistics are displayed correctly.

Written by the indexing model from the issue text.