[Feature] Saved papers list page and actions

## Source TODO
- 前端：收藏列表页面组件

## Scope
- Implement `web/src/components/research/SavedPapersList.tsx`
- Consume `GET /api/research/papers/saved`
- Support sort `judge_score | saved_at | published_at`
- Add open-detail and status action entry points

## Acceptance Criteria
- Saved papers render with pagination/limit
- Sorting works and is testable
- Empty and loading states are handled