Adds a runWithStdin method to AppProcess that accepts string,
Uint8Array, or Stream<Uint8Array> and feeds it to the child process
stdin while preserving the rest of the Command options. Internally
the method delegates to the same collect-and-exit body as run.
Replaces the bespoke gitWithStdin spawn helper in snapshot (ignore,
drop, stage, cat-file --batch) with calls to runWithStdin, and
migrates the Linux/Windows clipboard write paths (wl-copy, xclip,
xsel, powershell) off util/process.ts.
Kit Langton
ed580ec051