Alternative keybindings for command/prompt mode navigation

[delafthi]

Currently, Helix uses Ctrl+n/Ctrl+p and the up/down arrow keys to navigate command history in the command/prompt mode. While this works, I find myself rarely using command history navigation and would prefer a workflow more similar to Fish shell's completion behavior.

Current behavior

• Ctrl+n/Ctrl+p and arrow keys always navigate command history
• Autocompletion menu is shown by default as you type
• Autocompletion is navigated using the tab/backtab keys

Proposed behavior

The keybindings would adapt based on context:

Default state (no completion menu active):

• Ctrl+n/Ctrl+p and arrow keys: Navigate command history (as currently)

When Tab is pressed (entering completion menu; preferably this key would be configurable):

• Ctrl+n/Ctrl+p and arrow keys: Navigate the autocompletion menu (also left and right arrow keys)
• Esc: Exit/close the autocompletion menu, returning to default keybindings

This would make the workflow more intuitive for users coming from Fish shell, where the same keys adapt their behavior based on whether you're navigating completions or history.

Would this be something worth considering? I'm happy to work on a PR if there's interest in this approach.