lock: pin transient to magit master, drop monet/websocket
Magit master uses `transient--get-format' (transient 0.13+); Emacs 31
ships transient 0.12. Add a twist recipe pointing at magit/transient
plus a root `use-package' so `nix run .#lock --impure' resolves it.
Drop monet and websocket inputs — no longer referenced.