fix(bash): clean up background process groups

[yan-ad]

Summary

• terminate remaining process-group members after the foreground shell exits
• avoid hanging on stdout/stderr pipes inherited by background Node or shell processes
• add a regression test covering successful commands that leave a background process

Validation

• cargo fmt --all
• cargo check --bin crabcode
• git diff --check

Test note

The full test target is currently blocked by pre-existing input.render(...) test call sites that are missing a newly required boolean argument.

[yan-ad]

@Blankeos, could you please review this PR when you get a chance? This fixes leaked background processes that can accumulate and cause excessive memory usage. Thank you!

[Blankeos]

Maintainer update

Merge confidence: 5/5

Merged main into this branch (cab551c → 8b1f4c4) so it is no longer ~23 commits behind.

What I did

• Merged origin/main into fix/acp-background-process-cleanup (clean merge, no conflicts)
• Verified cargo check succeeds on the merged tip
• Re-ran bash tool regressions:
  • successful_command_kills_background_processes ✅
  • interactive_read_receives_eof_instead_of_hanging ✅
• Manual orphan smoke (process-group mirror of the tool):
  • OLD (wait shell only, no killpg): sleep 60 & left a live orphan ✅ reproduces bug
  • NEW (wait + killpg): orphan gone ✅
• No additional code changes to the bash cleanup logic itself — the original fix still stands

CI note
Repo workflows here are Release/Publish only. On this PR, plan is green and artifact jobs are skipped — there is no cargo test gate to wait on.

Why this PR is necessary
On main, success path never killpgs; only timeout/abort does. Background jobs from the bash tool (cmd &) leak. This captures PGID at spawn and kills the group when the foreground shell exits.

Ready to merge.

[Blankeos]

Thank you again yan-ad, I really appreciate this!