Belief/Trade reorg: refresh index with canonical layout

INDEX.json

@@ -3,15 +3,16 @@
     "Belief",
     "Trade"
   ],
-  "legacy_aliases": [
-    "Faith",
-    "v1",
-    "v2"
+  "canonical_layout": [
+    "source",
+    "splits",
+    "benchmark_direct",
+    "benchmark_profile",
+    "benchmark_retrieval",
+    "metadata"
   ],
-  "notes": "Belief replaces Faith as canonical name for belief-level data.",
-  "mappings": {
-    "Faith/*": "Belief/*",
-    "v1/*": "Belief/* (canonical via organized subtrees)",
-    "v2/*": "Trade/* (canonical via organized subtrees)"
-  }
+  "trade_extra": [
+    "support_set"
+  ],
+  "legacy_root": "legacy/"
 }