- Add handlers_tasks.go: TasksDeps, TaskNewFormHandler, TaskCancelNewHandler, TaskCreateHandler, TaskShowHandler, TaskDeleteConfirmHandler, TaskDeleteHandler, plus stub Edit/Update/Reorder handlers
- Add task routes to router.go (static before parametric per Pitfall 1)
- Add TasksDeps param to NewRouter; update main.go and all test callers
- Move TaskColumns/TaskColumnLabels to templates package to avoid import cycle