[Feature Request] Add vi mode support for navigation and text selection

**Feature Description**
implement vi mode, especially in two cases: 1) being able to cycle through options wiht J/K for example 2) being able to exit bottom text field, and navigate conversation with vi commands, especially for selecting and copying stuff.

**Environment Info**
- Platform: darwin
- Terminal: tmux
- Version: 2.1.267
- Feedback ID: 9e91abf8-c7ec-48eb-8d1c-62f428f354d7

Start by locating the terminal input, option-navigation, and conversation text-selection entry points; the issue does not name specific files or tests. Determine how key modes and copying currently work, then define completion around J/K option cycling, leaving the bottom text field, and vi-style conversation navigation and selection.

Written by the indexing model from the issue text.