Add API Q1 CAPA: root cause, corrective action gate, effectiveness verification

Implements tester feedback against API Q1 §5.9.1.2 / §6.4.2:

- Root Cause field + 6M Root Cause Category lookup (Man/Machine/Method/
  Material/Measurement/Environment), separate from Deviation Detail/Category
- "Corrective Action Required?" Yes/No gate on every NCR with a required
  justification
- Corrective action plan with owner + due date; owner is notified by email
- Effectiveness verification (result, notes, server-stamped verifier/date)
  required before an NCR can close when corrective action is required —
  costing returns 409 listing the missing pieces
- Recurring-issue flag with bidirectional NCR-to-NCR links; prior NCRs show
  a warning when later NCRs reference them
- Dashboard metrics: % root cause completed, % CAPA verified effective,
  avg CAPA close time, overdue CAPA count, NCRs by root cause category
- CAPA section in the NCR detail UI, printable PDF, CSV export, and the
  vw_ncr_full Power BI view; admin list manager for root cause categories
- Migrations 0003 (schema + seeded 6M lookup) and 0004 (view refresh);
  demo seed data exercises every metric

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/tests/test_permissions.py

@@ -73,6 +73,15 @@ async def test_admin_can_act_at_every_stage(client, team):
         headers=hdr(team["admin"]),
     )
     assert r.status_code == 200
+    r = await client.post(
+        f"/api/ncrs/{ncr['id']}/capa",
+        json={
+            "corrective_action_required": False,
+            "corrective_action_justification": "Isolated incident; no systemic cause.",
+        },
+        headers=hdr(team["admin"]),
+    )
+    assert r.status_code == 200
     r = await client.post(
         f"/api/ncrs/{ncr['id']}/costing",
         json={"labor_cost": "1", "material_cost": "1", "service_cost": "1", "other_cost": "1"},