TODO: Add archived status to TODO note_type

TODO note_type only allows status values open and done. Need an archived status for TODOs that have been absorbed into a plan but whose underlying work isn't complete yet.

Why: When a TODO is scoped into a plan phase, the TODO's job (capture + triage) is done, but the work isn't. Marking it done is semantically wrong. We need archived (or absorbed) to distinguish "captured into plan" from "work completed."

Also consider: Adding a plan_slug field to the note schema so TODOs can explicitly link to the plan that owns them. Enables orphan detection query: "show me all TODOs not assigned to a plan."

Workaround for now: Using status=done + parent_slug=plan-* to indicate absorption.