refactor(jobs): address code review feedback on fp.job (Task 1.4)

- Move NOTE comment from between @api.depends and the function
  into a proper docstring on _compute_costs.
- Make currency_id required=True (default still in place — only
  a programmatic write would null it, but Monetary fields need a
  non-null anchor).
- Add test_current_location_for_confirmed to cover the title-case
  fallback branch in _compute_current_location.

Manifest 19.0.8.3.0 → 19.0.8.3.1.

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/test_fp_job_state_machine.py

@@ -86,3 +86,9 @@ class TestFpJobStateMachine(TransactionCase):
         self.assertEqual(job.actual_cost, 0.0)
         self.assertEqual(job.margin, 1000.0)
         self.assertEqual(job.margin_pct, 100.0)
+
+    def test_current_location_for_confirmed(self):
+        job = self._make_job()
+        job.action_confirm()
+        # Forces compute via field read; expect title-cased state
+        self.assertEqual(job.current_location, 'Confirmed')