feat: add vim keybindings

[christianascone]

I’ve added Vim-style keybindings for basic navigation: up, down, left, right, as well as for scrolling up and down.

Keybindings Added

• h - Move left
• j - Move down
• k - Move up
• l - Move right
• Ctrl + u - Scroll up
• Ctrl + d - Scroll down

These bindings are added in addition to the existing keys, so no current functionality is changed.

Motivation

As a Vim/Tmux user, I thought these keybindings would be helpful for others who are used to navigating this way. I checked and confirmed that they don’t conflict with any existing hotkeys, so they should fit in without disrupting other shortcuts.

[aarondfrancis]

This is awesome. Thank you so much! I'm gonna rework hotkeys real quick to make them more flexible, so I'll bring your PR up to date here in a sec

[neilgilmour]

Nice one @christianascone! Thank you. How about shift + j/k for the big scrolls?

[christianascone]

Thank you!
I had thought about it, but I mapped the "big scroll" to Ctrl-D and Ctrl-U, since those are the defaults for half-page movements in Vim.

[aarondfrancis]

working on this in #4! Closing this one for now. Thank you!