02 — Flat Tasks in a List

What to build: Opening a List shows its Tasks. The user can add a Task (title + optional note), edit its title and note, complete it, and reopen it. Completed Tasks are kept forever but hidden by default; a "show completed" toggle reveals them. No nesting in this slice — every Task is top-level.

Blocked by: 01 — Walking skeleton.

Status: done (commit fc61bea, 2026-08-04)

☐ User can add a Task with a title, and optionally a note, from the List page
☐ User can edit a Task's title and note
☐ User can complete and reopen a Task; completion timestamp is stored
☐ List view shows only open Tasks by default; a toggle reveals completed ones
☐ Completed Tasks are never deleted by any action in this slice
☐ Tests cover add, edit, complete, reopen, and the hidden/shown behaviour