ListService: 352-line CRUD layer with 25-finding TDD audit
Shipped the service layer for Unified Lists (PR #288): 352-line ListService with create, read, update, archive operations enforcing user isolation. Three TDD audit rounds caught 25 findings—security issues (missing RLS restore), type-safety degradations (ValidationInfo → object), and logic bugs (empty update → false 404). Completes the three-part infrastructure: migration → models → service.