Belief/Trade reorg: add unified metadata folder for Trade

Trade/metadata/benchmark_retrieval_metadata.json

@@ -0,0 +1,16 @@
+{
+  "version": "retrievalgen_v2_top5_market_noprofile",
+  "description": "RetrievalGen benchmark without wallet profile. CurrentMarketHistory + RetrievedMarketTraces (Top5 same-market neighbors).",
+  "rows": {
+    "test": 59559,
+    "validation": 114471
+  },
+  "retrieval": {
+    "scope": "same market",
+    "top_k": 5,
+    "neighbor_trades": "all trades before current sample time",
+    "causality": "strictly before current sample time (block, log_index)",
+    "similarity": "0.4 act + 0.2 outcome + 0.2 price + 0.15 size + 0.05 tempo"
+  },
+  "support_set": "v2/support_set"
+}