Fix incident worker redispatch and PR fallback

[1612535983]

Summary

• allow incident_new/regressed runs to resume the incident thread and redispatch stale worker tasks
• create a PR automatically when a worker returns branch_name/commit_sha but no pr_url
• ignore the large Kimi image tarball artifact

Tests

• ECOMMERCE_LOG_FILE= uv run pytest -q tests/test_auto_review_merge.py tests/test_api_integration.py::test_worker_completion_uses_auto_review_when_enabled tests/test_incident_auto_dispatch.py