feat: support sending to pi running in Neovim terminal

[diidiiman]

When pi is started inside a Neovim terminal (:term pi), the unix socket sometimes fails to be correctly discovered or connected to, resulting in ENOENT errors when attempting to send prompts, files, or selections.

This PR adds a fallback mechanism inside M.prompt. Before attempting to connect via the socket, it scans the active Neovim buffers to see if there is a terminal buffer running pi. If one is found:

1. It focuses the terminal (or opens it in a split if it is currently hidden).
2. It sends the message payload using bracketed paste (\x1b[200~ ... \x1b[201~) to correctly handle multiline selections.
3. It appends \r to submit the prompt directly.

This matches the behavior of similar plugins (like gemini-cli.nvim) and allows a seamless experience when users prefer to keep pi docked inside Neovim.

[carderne]

Thanks for this @diidiiman sorry for the really slow response but merging now!