feat(sisyphus-task): inherit parent model for categories and show fallback warning

- Change model priority: user override > parent model > category default
- Add ModelFallbackInfo to track model resolution type
- Show warning toast when category uses inherited or default model
- Add tests for model fallback info in task toast

src/features/task-toast-manager/index.ts

@@ -1,2 +1,2 @@
 export { TaskToastManager, getTaskToastManager, initTaskToastManager } from "./manager"
-export type { TrackedTask, TaskStatus, TaskToastOptions } from "./types"
+export type { TrackedTask, TaskStatus, TaskToastOptions, ModelFallbackInfo } from "./types"