fix(kanban): a superseded task reads as unknown #1002

Problem

A task document with status: superseded lands in the unknown column of aidd kanban: kanban/src/domain/models/progress-status.ts does not map it. 27 task files already use it, and #993 adds 13.

Scope

• Map superseded to a closed state, next to done.

Acceptance criteria

• A plan with status: superseded no longer shows as unknown in aidd kanban.
• A test pins the mapping.