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

pkg/models/task.go

@@ -5,11 +5,11 @@ import "time"
 type TaskStatus string
 
 const (
-	StatusPending   TaskStatus = "pending"
-	StatusRunning   TaskStatus = "running"
-	StatusSucceeded TaskStatus = "succeeded"
-	StatusFailed    TaskStatus = "failed"
-	StatusCancelled TaskStatus = "cancelled"
+	StatusTodo       TaskStatus = "todo"
+	StatusInProgress TaskStatus = "in_progress"
+	StatusInReview   TaskStatus = "in_review"
+	StatusDone       TaskStatus = "done"
+	StatusWontdo     TaskStatus = "wontdo"
 )
 
 type Task struct {
@@ -60,3 +60,8 @@ type UpdateTaskRequest struct {
 type CommentRequest struct {
 	Body string `json:"body"`
 }
+
+type CompleteTaskRequest struct {
+	Result       string `json:"result"`
+	ErrorMessage string `json:"errorMessage,omitempty"`
+}