Add auto-update for curl-installed CLI binaries

[yahanxing-stripe]

Summary

When the CLI is installed via curl, it now:

• Checks for updates synchronously after each command completes, rate-limited to once per day
• Applies pending updates at the start of the next invocation: downloads the new binary, verifies SHA256 checksum, atomic file swap, and re-execs so the user always runs the latest version
• Skips major version changes — only minor/patch updates are auto-applied to avoid silent breaking changes
• Only affects curl-installed binaries — Homebrew, apt, Scoop, and npm users are unaffected

User-facing output

  Automatically updating Stripe CLI from 1.23.0 to 1.23.1.
  To disable auto-update, set STRIPE_NO_AUTO_UPDATE=1 or add auto_update = false to ~/.config/stripe/config.toml
  Updated successfully ✓

####Opt-out

  # ~/.config/stripe/config.toml
  [settings]
  auto_update = false

Or:

export STRIPE_NO_AUTO_UPDATE=1