fix(quick-push): align fast mode with shell environment

[markwylde]

Summary

• run Quick Push git and gh commands with the same shell-derived environment used for AI providers, so tools such as Homebrew gpg are available from Electron
• include changed file contents for tracked and untracked files in the fast-mode prompt instead of only including untracked file contents

Verification

• npm run build:app
• npm run lint