feat(tui): match model switcher to new designs - #56095

Matches the model switcher to the new designs.

DialogSelect

• Options can carry a detail, shown below the list while the option is selected. It's a string or a render function; a function is called each time the option becomes selected, because a rendered element cannot be shown again once it is removed. The row is reserved whenever any option has a detail, so the dialog does not resize while you move.
• Action titles can be a function of the selected option.

Model switcher

• Detail row: price ($4/$20 or Free) on the left. Input modalities, context window and reasoning support on the right, separated by ·.
• Favorites: a blue * replaces the old "(Favorite)" label. The action reads favorite or unfavorite depending on the selected row.
• No reordering: favoriting no longer moves rows. The list order is fixed when the dialog opens.
• Search results: the provider shows inline instead of on the right.

The model sort now uses an explicit free flag instead of comparing the right-hand label to "Free". Tests are updated to match.

Gated behind the new-designs experiment. Stacked on #56094.