Feat/enhance copy mode

[BrettKulp]

fixes the flashing issue when entering copy mode and cursor sometimes not visible when entering copy mode in #79 for #50 and synced with recent changes

add ctrl + w j/k for entering and exiting copy mode without scrolling the chat history. The cursor will enter into a row that is already visible in the chat history if the chat is scrolled up to previous older messages. Leader + v, esc, and q still scroll chat history while entering and exiting as before.

Entering and exiting copy mode via ctr + w + j/k if will enter into a visible section of chat history

[leohenon]

This is better, but I still see a few issues:

• Ctrl+W pending state is never cleared, so pressing something like Ctrl+W x can stay stuck pending.

• Using hasModifier(event) also captures Alt+W / Meta+W / Super+W instead of only Ctrl+W.

• README says visual y stays in copy mode, but the implementation still exits copy mode after yanking, which is correct but the README should be updated.

• This includes changes unrelated to copy mode, please rebase and keep only relevant changes.