feat: add data layer __init__.py

alpha_factory/data/__init__.py

@@ -0,0 +1,17 @@
+"""
+Data layer — canonical BRAIN field registry, operator catalog, and group keys.
+This is the pipeline's ground truth for what's available on the platform.
+"""
+from .brain_fields import (
+    ALL_FIELDS, FIELD_INDEX, GOLDMINE_FIELDS, TIER1_MODEL77_FIELDS,
+    pick_field, get_backfill_days, get_sign_multiplier,
+    BrainField, SignConvention, DatasetTier,
+)
+from .brain_groups import ALT_GROUPS, PRODUCTION_GROUPS, pick_group, get_group_for_expression
+
+__all__ = [
+    "ALL_FIELDS", "FIELD_INDEX", "GOLDMINE_FIELDS", "TIER1_MODEL77_FIELDS",
+    "pick_field", "get_backfill_days", "get_sign_multiplier",
+    "BrainField", "SignConvention", "DatasetTier",
+    "ALT_GROUPS", "PRODUCTION_GROUPS", "pick_group", "get_group_for_expression",
+]