* feat: add configurable done flag to TODO states
* feat: stamp CLOSED for any configured done state
* feat: add DONE state option and done marker to settings
* chore: remove unused Item.CycleState
* chore: drop vestigial state constants, mention DONE add in settings help
* feat: add state form model and commit logic
* feat: wire state form update/view into settings dispatch
* feat: replace state add/edit with unified form, toggle done after creation
* consolidate AddState and AddDoneState
* add findState() helper