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

Makefile

@@ -2,11 +2,13 @@
 
 BINARY_API := bin/forgebot-api
 BINARY_OP  := bin/forgebot-operator
+BINARY_TUI := bin/forgebot-tui
 VERSION    ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo "0.0.0-dev")
 
 build: tidy
 	go build -ldflags="-s -w" -o $(BINARY_API) ./cmd/api
 	go build -ldflags="-s -w" -o $(BINARY_OP) ./cmd/operator
+	go build -ldflags="-s -w" -o $(BINARY_TUI) ./cmd/tui
 
 test:
 	go test -race -count=1 ./pkg/... ./internal/... ./api/...