fix: jobs-v2 program runs can leave background children running after a successful command exits

[sam-saffron-jarvis]

What changed

• Jobs-v2 program runs now use the same process cleanup helper as the shell tool, so cleanup always best-effort kills the command process group and nonce-tagged descendants after the command returns.
• Restored the jobs-v2 program runner's existing WaitDelay after installing the shared cleanup helper, preserving the runner's prior wait-delay behavior.
• Added a regression test for a successful shell command that backgrounds a long-lived child, writes its PID, and exits immediately; the test asserts the child is gone after Run returns.

Why this is high-value

Jobs-v2 is a daily automation path for Jarvis. Before this change, a successful program command could launch a background child and exit cleanly, causing Jarvis to mark the job successful while the child kept running indefinitely. Repeated scheduled runs could accumulate orphaned CPU/memory/file-handle consumers and make later operations harder to reason about.

Validation

• Reproduced the failure with the new regression test before the fix: the background sleep process remained alive after Run returned.
• gofmt -w cmd/serve_jobs_v2.go cmd/serve_jobs_v2_program_test.go
• go build ./...
• go test ./...
• go test ./cmd -run TestJobsV2ProgramRunner_CleansUpBackgroundChildOnSuccess -count=5
• git diff --check

[SamSaffron]

Closing after manually bringing the validated changes into the working copy.