Add TUI kanban board, review workflow, and new task statuses

Replace task statuses (pending/running/succeeded/failed/cancelled) with
a kanban workflow: todo → in_progress → in_review → done/wontdo.

When a non-review agent task completes, the API auto-creates a child
review task and moves the parent to in_review. Only humans can move
tasks from in_review to done/wontdo via the TUI.

New components:
- cmd/tui: bubbletea kanban board with $EDITOR integration
- POST /api/v1/tasks/{id}/complete: agent completion callback
- Operator --api-url flag for completion callbacks
- ProviderQueue sets tasks to in_progress on pickup
- AgentTask reconciler calls /complete on job finish

internal/apiserver/server.go

@@ -59,6 +59,7 @@ func (s *Server) routes() chi.Router {
 		r.Post("/tasks", tasksH.Create)
 		r.Get("/tasks/{id}", tasksH.Get)
 		r.Patch("/tasks/{id}", tasksH.UpdateStatus)
+		r.Post("/tasks/{id}/complete", tasksH.Complete)
 		r.Post("/tasks/{id}/comment", tasksH.PostComment)
 	})