[Feature Request] Add Vim visual mode support (v/V/Ctrl+V) to input editor

Question

**Bug Description**
Please add vim visual mode support (v / V / Ctrl+V) to the input editor. Currently there's no way to select an arbitrary range of text in vim mode. Text objects only cover structured cases (words, quotes, brackets), and the external editor workaround clears the terminal display, losing conversation context. Visual mode is a core vim workflow — without it, vim mode is significantly less usable for vim users.

**Environment Info**
- Platform: darwin
- Terminal: iTerm.app
- Vers