[FEAT] Allow setting a project default work-item state

[martian56]

Type / Priority

Feature / Medium

Summary

A project's default work-item state cannot be set; the column is dead.

Current state (evidence)

• DefaultStateID exists (api/internal/model/project.go:59) but service/project.go Update (:100-166) never sets it, handler/project.go never binds default_state_id, and there is no UI control. (Default assignee works end-to-end; default state does not.)

Proposed scope

Add default_state_id to Update service+handler (mirror the defaultAssigneeIDSet nullable pattern) and a default-state dropdown in General settings. Pairs with the auto-close close-state target.