Belief/Trade reorg: move legacy aux files into metadata

Belief/metadata/split_config_v1.json

@@ -0,0 +1,32 @@
+{
+  "version": "v1",
+  "seed": 20260318,
+  "experiment_wallets_file": "wallet_ids_diverse_nonoverlap_2000_seed20260318.txt",
+  "experiment_wallets": 2000,
+  "split_ratios": {
+    "train": 0.7,
+    "validation": 0.15,
+    "test": 0.15
+  },
+  "time_order_keys": [
+    "stance_first_block",
+    "stance_last_block",
+    "market_id"
+  ],
+  "history_mode": "rolling within split construction",
+  "prompt_history_max_items": 30,
+  "counts": {
+    "train": {
+      "samples": 98094,
+      "wallets": 2000
+    },
+    "validation": {
+      "samples": 21147,
+      "wallets": 2000
+    },
+    "test": {
+      "samples": 22204,
+      "wallets": 2000
+    }
+  }
+}