Add support for suspending LazyGit with Ctrl+Z on Unix systems

[cowboy8625]

• PR Description

✨ Add Ctrl+Z suspend support for LazyGit on Unix-like systems

📝 Summary

This PR adds support for suspending LazyGit when the user presses Ctrl+Z, making it behave like common CLI tools (e.g., Vim, less, htop):

• Pressing Ctrl+Z sends a SIGTSTP signal to suspend LazyGit.
• After resuming with fg, LazyGit redraws and continues working without hanging.
• During suspension, background routines are paused to avoid running while LazyGit is stopped.

⚙ Implementation details

• Added a new suspendApp function triggered by a Ctrl+Z keybinding.

• Inside suspendApp, we do a runtime OS check (runtime.GOOS == "windows") and return early (effectively no-op) on Windows.
  This way, the keybinding itself is always defined cross-platform, but the suspend logic only runs on Unix-like systems.

• Integrated with the background routine manager:

  • Calls PauseBackgroundRefreshes(true) before sending the suspend signal.
  • Calls PauseBackgroundRefreshes(false) on resume (handled via SIGCONT).

• After resuming, LazyGit keeps running smoothly without hanging.

🧠 Design notes

• Considered using build tags / OS-specific Go files to fully exclude the suspend logic on Windows.
• Opted for a runtime check instead for simplicity, but happy to refactor to build-specific files if that’s the preferred approach.

✅ Motivation

Make LazyGit feel more native on Unix-like systems by supporting standard terminal suspend/resume (Ctrl+Z / fg) behavior.

• Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc

Closes #3906

[cowboy8625]

@stefanhaller I’ve addressed the earlier issues you pointed out. I’m not sure if a test is needed for this change, or if there are any other steps you’d expect before merging. Let me know! 🙂

[stefanhaller]

@cowboy8625 The behavior is still the same for me, as described in #3906 (comment). After typing bg, I get the "+ suspended (tty output)" error, and then fg hangs.

(We had a similar problem back when we used $SHELL -i for running custom shell commands; see #3903 (comment) for some discussion. Not sure how much of a connection there is between the two cases; just mentioning it.)

And finally, when I use make run to start lazygit, then ctrl-z doesn't work at all; lazygit does suspend, but the shell prompt doesn't appear. This may be only relevant for developers, not users, but the same could happen for users if they launch lazygit through a wrapper script. I suppose in this case we'd have to send the SIGTSTP to the wrapper script (or to the make process in my case), not to lazygit; but I'm not sure what the criterion for that is. Walk the chain of parent processes until we find one whose name matches $SHELL?

Until these problems are solved I don't feel we can merge this. But I'm also not sure how much time is justified for putting into this, to be honest.