Belief/Trade reorg: refresh dataset card with canonical layout

DATASET_CARD.md

@@ -1,13 +1,17 @@
-# UserModeling Dataset (Belief / Trade)
+# UserModeling Dataset (Canonical: Belief / Trade)
 
-Canonical organization:
+## Canonical tiers
+- `Belief/` (belief-level)
+- `Trade/` (trading-level)
 
-- `Belief/` (belief-level tasks; formerly v1 / Faith)
-- `Trade/` (trading-level tasks; formerly v2)
+## Canonical internal layout
+Each tier follows (when available):
+- `source/`
+- `splits/`
+- `benchmark_direct/`
+- `benchmark_profile/`
+- `benchmark_retrieval/`
+- `metadata/`
 
-Legacy compatibility folders may still exist:
-- `v1/`, `v2/`, `Faith/`
-
-Preferred paths for new usage and citations:
-- `Belief/*`
-- `Trade/*`
+Additional: `Trade/support_set/` for retrieval candidate pool.
+Legacy copies are stored under `legacy/`.