F09: Dashboard sorting and filtering

## What to build

Add sorting and filtering controls to the dashboard so users can organise the chore list by status, pack, XP value, due date, etc., and narrow it down to a subset of chores.

## Acceptance criteria

- [ ] Sort by: name, pack, XP (ascending/descending), due date, completion status
- [ ] Filter by: pack, status (due, overdue, completed today, all), XP range
- [ ] Sort and filter state persists across sessions
- [ ] "Clear filters" button resets to default view
- [ ] Sorting/filtering works on both mobile and desktop layouts

## Blocked by

None — can start immediately