Belief/Trade reorg: add unified metadata folder for Trade

Trade/metadata/source_metadata.json

@@ -0,0 +1,18 @@
+{
+  "version": "v2_source_metadata_v1",
+  "files": [
+    {
+      "path": "v2/v2_behavior_features_merged_pospnl_kline_v2_fixcost.parquet",
+      "alias": "behavior_fixcost.parquet"
+    },
+    {
+      "path": "v2/v2_trade_price_matched_pre80m_cap30.parquet",
+      "alias": "trade_price_matched.parquet"
+    },
+    {
+      "path": "v2/v2_market_semantic_from_behavior_cap30_pricecovered.parquet",
+      "alias": "market_semantic.parquet"
+    }
+  ],
+  "note": "Source parquet files already exist under v2/ root in this repo."
+}