Fix bounded idempotent batch retries

[chubes4]

Summary

• adopt existing pending v2 chunk actions by exact hook, arguments, and group identity
• persist a bounded per-item attempt count and terminal failed state
• fail pipeline and task batch parents deterministically when an item exhausts its retry budget
• converge the attempts column on existing installs

Closes #3434

Verification

• php tests/batch-scheduler-retry-budget-smoke.php (20 passed)
• php tests/fanout-adoption-recovery-smoke.php (10 passed)
• php tests/batch-completion-strategy-smoke.php (all pass)
• php tests/task-scheduler-batch-parent-link-smoke.php (all pass)
• PHP syntax checks for all changed PHP files
• git diff --check

Homeboy WordPress lint was invoked but did not return within the local two-minute client window.

AI assistance

OpenAI gpt-5.6-sol via OpenCode/Homeboy implemented and verified the bounded idempotent retry repair.