Better display for long checklists in Pi

Currently Pi caps widget output at 10 lines. This becomes a problem when there are more than 10 checklist items. After the 10th item is complete, there is effectively no progress to be displayed and it's hard to tell what the agent is currently doing. Below is a proposed solution.

Suppose there are 15 items on the checklist

- [ ] Item 01
- [ ] Item 02
- [ ] Item 03
- [ ] Item 04
- [ ] Item 05
- [ ] Item 06
- [ ] Item 07
- [ ] Item 08
- [ ] Item 09
- [ ] Item 10
- [ ] Item 11
- [ ] Item 12
- [ ] Item 13
- [ ] Item 14
- [ ] Item 15

First, it would start by showing the first 9 items as they are checked off

- [x] Item 01
- [ ] Item 02
- [ ] Item 03
- [ ] Item 04
- [ ] Item 05
- [ ] Item 06
- [ ] Item 07
- [ ] Item 08
- [ ] Item 09
- [ ] Item 10

...

- [x] Item 01
- [x] Item 02
- [x] Item 03
- [x] Item 04
- [x] Item 05
- [x] Item 06
- [x] Item 07
- [x] Item 08
- [x] Item 09
- [ ] Item 10

Then, the list would scroll so the next unchecked item is always visible.

- [x] Item 02
- [x] Item 03
- [x] Item 04
- [x] Item 05
- [x] Item 06
- [x] Item 07
- [x] Item 08
- [x] Item 09
- [x] Item 10
- [ ] Item 11

This would move down one item as items are checked off.

- [x] Item 03
- [x] Item 04
- [x] Item 05
- [x] Item 06
- [x] Item 07
- [x] Item 08
- [x] Item 09
- [x] Item 10
- [x] Item 11
- [ ] Item 12

...

Until eventually the end of the list is reached.

- [x] Item 06
- [x] Item 07
- [x] Item 08
- [x] Item 09
- [x] Item 10
- [x] Item 11
- [x] Item 12
- [x] Item 13
- [x] Item 14
- [x] Item 15

Start at the Pi widget rendering path and trace how checklist output is capped at 10 lines. Implement the proposed scrolling window so the next unchecked item remains visible while preserving the 10-line limit. Done means long checklists continue showing progress as items are completed through the end of the list.

Written by the indexing model from the issue text.