Issue description

This is a feature request, not a bug report.

I use choose-tree -wZ with a custom -F format that colors tree list entries based on window name suffixes using #[] directives. This works well for the text labels in the tree list.

However, the mini preview panes shown for each window in choose-tree have a central badge/label (showing window index/name) that uses hardcoded styling. There is no way to customize the badge color per-window.

Requested feature (any would solve the use case):

1. A format option for choose-tree preview badges, allowing #[] style directives with access to #{window_name} or user options.
2. A style option scoped to the preview badge only — window-style tints the entire pane content, which is too aggressive for this purpose.
3. A per-window background color for choose-tree previews only — something like a choose-tree-preview-style that colors the preview background without affecting the actual pane during normal use.

Use case: I run 10+ tmux windows with different status states indicated by window name suffixes. The tree list labels are color-coded via -F, but when scanning the mini-preview grid, all badges look identical. Per-window badge or background styling
would make it faster to identify windows needing attention.

Required information

Please provide the following information. These are required. Note that bug reports without logs may be ignored or closed without comment.

• tmux version: 3.3a
• Platform: Linux x86_64
• Terminal: WezTerm (via SSH)
• $TERM inside tmux: tmux-256color
• $TERM outside tmux: xterm-256color
• Logs: N/A (feature request, not a bug)