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/tui/styles.go

@@ -0,0 +1,37 @@
+package tui
+
+import (
+	"github.com/charmbracelet/lipgloss"
+
+	"git.unkin.net/unkin/forgebot/pkg/models"
+)
+
+var statusColors = map[models.TaskStatus]lipgloss.Color{
+	models.StatusTodo:       lipgloss.Color("3"),
+	models.StatusInProgress: lipgloss.Color("4"),
+	models.StatusInReview:   lipgloss.Color("5"),
+	models.StatusDone:       lipgloss.Color("2"),
+	models.StatusWontdo:     lipgloss.Color("8"),
+}
+
+var (
+	columnTitleStyle = lipgloss.NewStyle().
+				Bold(true).
+				Padding(0, 1)
+
+	cardStyle = lipgloss.NewStyle().
+			Border(lipgloss.RoundedBorder()).
+			Padding(0, 1)
+
+	cardSelectedStyle = lipgloss.NewStyle().
+				Border(lipgloss.ThickBorder()).
+				Padding(0, 1)
+
+	detailLabelStyle = lipgloss.NewStyle().Bold(true).Width(14)
+	detailValueStyle = lipgloss.NewStyle()
+
+	helpStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+	errStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("1"))
+
+	dimStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
+)