Add --key flag to navi widget for custom keybindings

[knpwrs]

Summary

• Adds a --key flag to navi widget so users can customize the keybinding without manually editing widget output
• Shell plugin scripts now use template placeholders (__NAVI_KEY__) that are populated at runtime with the default or user-provided value
• Updates widget documentation with examples

Usage

# zsh — bind to Ctrl+Space instead of Ctrl+G
eval "$(navi widget zsh --key '^ ')"

# bash
eval "$(navi widget bash --key '\C- ')"

# fish
navi widget fish --key '\c ' | source

Without --key, behavior is unchanged (defaults to Ctrl+G for most shells, Alt+H for elvish).

Context

Related to #837 — while that issue is about zellij support, it touches on the broader need to customize how navi integrates with different terminal environments. Ctrl+G is the default unlock for zellij.

The widget docs previously stated: "There's currently no way to customize the widget behavior out-of-the-box" — this text was added by the project creator in PR #480 (commit a8ddc13, April 2021). The PR body and comments are empty, and I couldn't find any related issues or discussion suggesting this was a deliberate design constraint rather than simply the state of things at the time.

Alternative approach

The same effect can be achieved today by rebinding after eval. For example in zsh:

eval "$(navi widget zsh)"
bindkey '^ ' _navi_widget
bindkey -r '^g'

This works because the widget's eval registers the _navi_widget function and zle widget — the subsequent bindkey calls just reassign the trigger key. The --key flag makes this a one-liner instead.

So as an alternative to this PR we can also update the docs.

Test plan

• navi widget zsh outputs bindkey '^g' (default preserved)
• navi widget zsh --key '^ ' outputs bindkey '^ '
• navi widget bash --key '\C- ' replaces both legacy and modern bind lines
• navi widget fish --key '\c ' replaces both normal and insert-mode binds
• navi widget nushell --key 'control:char_space' replaces modifier and keycode
• navi widget powershell --key 'Ctrl+Space' replaces Chord value
• navi widget elvish --key 'Ctrl-g' replaces binding key
• No __NAVI_KEY__ placeholders leak in any shell's default output
• cargo test passes

[alexis-opolka]

Hi, just to let you know that I'll check the PR tomorrow. Sorry for the long wait.

[knpwrs]

No problem. I'm working around it in my dotfiles for the time being: https://github.com/knpwrs/dotfiles/blob/441c9621777b1914553a59d498554e9887e47527/lib/navi.zsh

[alexis-opolka]

Since there has been some PRs with helpful features merged, I'm planning to try and test it before making a (pre-release/release) version out of it.

It will help on the side of debian's packaging since the new version removes dependencies and adds some useful features and bug fixes.

I don't really know for now, I'll make a decision tomorrow after thinking about it.