Add 27B TP A/B (deterministic ground-truth: does TP2 beat TP1 per-GPU)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

configs/examples/stopb_27b_ab/p3_tp4.json

@@ -0,0 +1,15 @@
+{
+  "observation": "TP4",
+  "diagnosis": "deterministic TP A/B point",
+  "config_patch": {
+    "env_patch": {},
+    "flag_patch": {
+      "tensor-parallel-size": 4
+    }
+  },
+  "expected_effects": [
+    "measure peak request_rate_per_gpu at this topology"
+  ],
+  "why_not_previous_failures": "n/a",
+  "should_stop": false
+}