feat: add full window preview

[michal-pielka]

Summary

Add toggle-preview-full action to display preview content taking the full TUI's space, similar to the file preview functionality in
mini.nvim plugin. This allows users to temporarily maximize the preview pane to occupy the entire fzf window for
better content inspection.

Changes

New Action: toggle-preview-full

Introduces a new keybindable action that toggles between:

• Item list: The item list with optional normal preview window
• Fullscreen preview mode: Preview occupies the entire window space, with a minimal status line at the bottom showing the selected file

Key Features

1. Full-window preview display: When activated, the preview content takes over the entire terminal space normally occupied
   by the item list, prompt, scrollbar etc.
2. Filename: A status line at the bottom displays the currently selected file/item name
3. State preservation: The original preview visibility state is saved when entering fullscreen mode and restored when exiting
4. Auto exit on prompt change: Automatically exits fullscreen preview mode when the user modifies the search prompt

Comparison between normal preview

Normal preview (on the side)

Full window preview

Demo

Usage Example

fzf --bind 'tab:toggle-preview-full'