oracle: 2D cases (Kirsch plane stress, Lamé plane strain and axisymmetric, rotating disc and cylinder, NAFEMS LE1 with quad8) and J2 uniaxial explicit

The pending 2D LE1 case becomes a real one; the plasticity cases stay
pending with what they still need (static J2 for the collapse pressure,
the transcribed measurements for the Taylor bar).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

tests/oracle/nafems-le1-plane-stress/expected.json

@@ -1,14 +1,30 @@
 {
- "title": "NAFEMS LE1 elliptic membrane with 2D plane stress elements",
+ "title": "NAFEMS LE1 elliptic membrane with 2D plane stress elements (quad8)",
  "kind": "benchmark",
- "source": "NAFEMS, The Standard NAFEMS Benchmarks, TNSB Rev. 3, October 1990, test LE1",
- "status": "pending",
- "requires": "2D plane stress elements (docs/elements.md)",
+ "source": "NAFEMS, The Standard NAFEMS Benchmarks, TNSB Rev. 3, October 1990, test LE1 (target σ_yy = 92.7 MPa at D); as reproduced in the Abaqus 2017 Benchmarks Guide, 'LE1: Plane stress elements—elliptic membrane'",
  "quantities": [
   {
    "id": "syy_D",
    "quantity": "σ_yy at D (2, 0)",
-   "value": 92.7
+   "measure": {
+    "command": "solve.probe",
+    "params": {
+     "step": "Load",
+     "at": [
+      [
+       2,
+       0,
+       0
+      ]
+     ]
+    },
+    "pointer": "/nodes/0/stress/1"
+   },
+   "value": 92.7,
+   "tolerance": {
+    "relative": 0.01
+   },
+   "reason": "the target is published to three figures; the stress extrapolated to the edge on a converged mesh adds a few tenths of a percent"
   }
  ]
 }