feat(jobs): add fp.job native model with state machine

Header model replacing mrp.production. mail.thread for chatter,
priority/state/deadline tracking, sequence WH/JOB/00001+. Tests
cover create, confirm, cancel, and forbidden double-confirm.

State machine:
  draft -> confirmed -> in_progress -> done
              v                          ^
          cancelled              (rework reverts here)
  on_hold can be entered from confirmed or in_progress.

Step relations come in Task 1.5; SO/recipe/portal/cost extension
fields come in Task 1.4.

Part of: native job model migration (spec 2026-04-25)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating/tests/__init__.py

@@ -1,2 +1,3 @@
 # -*- coding: utf-8 -*-
 from . import test_fp_work_centre
+from . import test_fp_job_state_machine