Belief/Trade reorg: add benchmark metadata

Belief/benchmark_direct/benchmark_metadata.json

@@ -0,0 +1,11 @@
+{
+  "benchmark": "benchmark_direct",
+  "tier": "Belief",
+  "format": "parquet",
+  "files": [
+    "train.parquet",
+    "validation.parquet",
+    "test.parquet"
+  ],
+  "note": "Canonicalized from legacy nested path benchmark_core_direct/"
+}