[FEATURE]:Preserve the TUI while waiting for a detached external editor

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem

When /editor or the editor keybinding launches an external editor,
OpenCode blanks its TUI while waiting for the editor process to exit.

For editors that run outside the current terminal, such as:

• nvr --remote-wait
• code --wait
• other GUI or remote editors

the terminal does not need to be released or cleared. Keeping the previous
OpenCode screen visible would preserve useful conversation context while editing.

Expected behavior

Optionally:

1. Preserve the last rendered TUI frame.
2. Stop accepting TUI input and suspend redraws.
3. Wait for the editor process.
4. Resume and fully redraw after the editor exits.

Proposed configuration

{
  "editor": {
    "preserve_tui": true
  }
}