feat: offer to update and restart when a new release is out

[brtkwr]

While ccs is open it now checks for a newer release, at startup and then hourly. When one exists, a box appears over the preview pane:

╭──────────────────────────────────────────────────╮
│                                                  │
│   ccs v0.25.0 is available (you have v0.24.1).   │
│                                                  │
│   Enter: update and restart    Esc: later        │
│                                                  │
╰──────────────────────────────────────────────────╯

• Enter runs brew update then brew upgrade ccs in the background (the header shows "updating to v0.25.0..."), then restarts ccs with the same arguments. If the upgrade fails, the error shows and ccs keeps running.
• Esc hides it for that version for the rest of the session. It comes back on next launch, or when an even newer version appears.
• For the first second after it opens it ignores all keys, so an Enter or Esc you were already typing can't answer it by accident.
• If ccs wasn't installed through Homebrew, the box only tells you a new version exists. Local dev builds never check.

The check reads where github.com/agentic-utils/ccs/releases/latest redirects to. That avoids the GitHub API, whose 60-requests-an-hour allowance for anonymous callers was already used up on this office IP when I tested.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JUmkVYwbkobda1AnHuwFDE