fix(tui): fix list wrap logic when it has a unfocusable item on the top

[dawndiy]

• I have read CONTRIBUTING.md.
• I have created a discussion that was approved by a maintainer (for new features).

At the Switch Model dialog, models were grouped by the provider. Each section has a unfocusable name of the provider.
If I go down when at the last item, it will come to the top model, but It will not come to the last model when I go up at the first item. Because there is a provider name ( a list item ) before the first model. The list wrap logic is not adapter this scene.
This PR fix list wrap logic in this scene.

[charmcli]

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[dawndiy]

I have read the Contributor License Agreement (CLA) and hereby sign the CLA.

[blouflab]

thanks for that - it is great, these little annoying things

[kujtimiihoxha]

@dawndiy thanks for the PR and the fix, I am wondering if it would be better to jump the viewport to the first un-selectable item instead of the selectable item so that we actually go to the top?

So for example here instead of hiding the Anthropic title we just go to the first item in the list.

[dawndiy]

@kujtimiihoxha thanks your reply. Of cause it would be better to show the un-selectable item (provider name in this case), it will more readable.

Let me describe my use case about this issue:
As you know, OpenRouter has many models and the list is longer than the height of the Viewport. When the model I want is at the end of the list, I need long-press the DOWN KEY to move the cursor to get the end of the list. If I press too long, the cursor will come to the top due to the list's wrapping logic. But because of this issue, I can't press the UP KEY to go back to the end, so I need long-press the DOWN KEY again... This is very annoying.

Following your advice, I believe the following 2 points are our final desired outcomes.

1. Come to the first selectable item from the end wrap should show the un-selectable item before it in the viewport if there has a un-selectable before it.
2. The viewport can show the first un-selectable item when the cursor at the first selectable item. And now press the UP KEY can back to the latest selectable item

And I found that I can add these code to the end of the scrollToSelectio function, and it can run as what I want.

	selectedIndex, ok := l.indexMap.Get(l.selectedItem)
	if ok && selectedIndex > 0 {
		prevItem, ok := l.items.Get(selectedIndex - 1)
		if ok {
			if _, ok := any(prevItem).(layout.Focusable); !ok {
				prevRendered, ok := l.renderedItems.Get(prevItem.ID())
				if ok && prevRendered.start < start {
					if l.direction == DirectionForward {
						l.offset = max(0, prevRendered.start)
					} else {
						l.offset = max(0, lipgloss.Height(l.rendered)-(prevRendered.end+1))
					}
				}
			}
		}
	}

It works, but I don't know if this is the correct way to fix this issue and match the 2 points above.
I need read more code about the list implementation to find an appropriate way to fix this, any ideas?