feat(fp.job): post-shop transition helpers (Tasks 2+3)

_fp_check_advance_post_shop: in_progress + all steps terminal →
  awaiting_cert (cert required) or awaiting_ship. Auto-spawns cert
  + delivery and fires notifications. Idempotent. Does NOT raise —
  gate failures bubble up via fp.job.step.button_finish (Task 4).
_fp_check_advance_after_cert_issue: awaiting_cert → awaiting_ship
  when every required cert is state=issued.
_fp_check_regress_after_cert_void: awaiting_ship → awaiting_cert
  when a previously-issued cert is voided. Re-notifies QM.

hasattr guards on _fp_schedule_cert_activity + _fp_resolve_cert_activities
keep this safe during incremental rollout — those land in Task 20.

Test scaffolding added covering helper existence + idempotency.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_jobs/tests/__init__.py

@@ -7,3 +7,4 @@ from . import test_blocker_compute
 from . import test_late_risk_ratio
 from . import test_active_step_id
 from . import test_autopause_cron
+from . import test_post_shop_states