Fix cleanup idle wrapper convergence

[chubes4]

Summary

• Treat empty pipeline_system_task wrapper descendants as terminal idle wrappers in cleanup status aggregation.
• Prevent cleanup runs from staying waiting_on_children forever when drain reports no runnable work remains.
• Add smoke coverage for the issue Cleanup status stays waiting on empty processing wrapper jobs #691 shape: processing parent, empty processing wrapper child, zero cleanup rows.

Fixes #691.

Verification

• php tests/smoke-worktree-cleanup-cli.php
• php -l inc/Cleanup/DataMachineJobCleanupRunEvidenceStore.php
• php -l tests/smoke-worktree-cleanup-cli.php
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Diagnosed the cleanup convergence failure, drafted the fix and smoke coverage, and ran local verification. Chris remains responsible for review and testing.

[homeboy-ci]

Homeboy Results — data-machine-code

Audit

✅ audit — passed

• audit — 10 finding(s)
• Total: 10 finding(s)

Deep dive: homeboy audit data-machine-code --changed-since 92c0dfa

Artifacts and drill-down

• CI results artifact: homeboy-ci-results-data-machine-code-audit-quality-Linux-node24 contains immediate command JSON for this action invocation.
• Observation artifact: homeboy-observations-data-machine-code-audit-quality-Linux-node24 contains exported Homeboy run history for deeper queries.
• Drill-down: download the observation artifact, then run homeboy runs import <dir>, homeboy runs list, and homeboy runs findings <run-id>.
• Artifacts are attached to the workflow run: https://github.com/Extra-Chill/data-machine-code/actions/runs/27472439592

Tooling versions

• Homeboy CLI: homeboy 0.229.0+0f21fd5
• Extension: wordpress from https://github.com/Extra-Chill/homeboy-extensions
• Extension revision: 838830a8
• Action: unknown@unknown