git stderr ('not a git repository') leaks to terminal when working outside a repo #1

Symptom

Running pify/yolo in a folder that is not a git repository prints git fatal messages to the terminal:

fatal: not a git repository (or any of the parent directories): .git

This happens on every risky bash/powershell command and on /yolo rewind because git is called without suppressing stderr. The extension already catches the error (gitHead returns null; decideCheckpoint returns {failed:true}), but stderr still leaks.

Fix

Pass stdio: ["ignore", "pipe", "ignore"] to the 5 execFileSync("git", ...) calls in extensions/yolo.ts (gitHead, gitCheckpoint runGit + update-ref, releaseRefs, /yolo rewind restore). Stdout keeps working; only stderr is silenced.

A PR with the same fix is proposed in #2