Emit OSC 133 escape sequences to mark prompts

Many terminals now support commands and keybindings to navigate shell prompts as marked by OSC 133 escape sequences.

• Ghostty: https://ghostty.org/docs/config/keybind/reference#jump_to_prompt
• Kitty: https://sw.kovidgoyal.net/kitty/shell-integration/
• PowerShell: https://learn.microsoft.com/en-us/windows/terminal/tutorials/shell-integration#powershell-pwshexe
• VS Code: https://code.visualstudio.com/docs/terminal/shell-integration
• Neovim: https://neovim.io/doc/user/terminal.html#terminal-osc133 (where I got some of the links above)

A spec can be found here but the gist is:

The start of a prompt is marked by sequence OSC 133 ; A ST, and the end by OSC 133 ; B ST.

(Again copied from Neovim docs.)

Claude Code could mark prompts in this way to make it easier to navigate the chat.