Problem: The NDJSON spawn path had no stdin support, so `M.submit` used
one-shot `vim.system()` with no live feedback. Status events from the
scraper were never surfaced to Neovim.
Solution: Conditionally create a `stdin_pipe` in the NDJSON path and
write `opts.stdin` after spawn. Switch `M.submit` to `ndjson=true`; route
`ev.status` events to a new `on_status` callback and `ev.success` to the
existing `callback`. A `done` flag prevents double-callback on crash.
Barrett Ruth
ecbe60cbd8
