feat(CORE-002): add GLD share quote conversion seam

app/domain/__init__.py

@@ -5,9 +5,16 @@ from app.domain.backtesting_math import (
     asset_quantity_from_money,
     materialize_backtest_portfolio_state,
 )
+from app.domain.instruments import (
+    asset_quantity_from_weight,
+    instrument_metadata,
+    price_per_weight_from_asset_price,
+    weight_from_asset_quantity,
+)
 from app.domain.portfolio_math import (
     build_alert_context,
     portfolio_snapshot_from_config,
+    resolve_portfolio_spot_from_quote,
     strategy_metrics_from_snapshot,
 )
 from app.domain.units import (
@@ -35,5 +42,10 @@ __all__ = [
     "decimal_from_float",
     "portfolio_snapshot_from_config",
     "build_alert_context",
+    "resolve_portfolio_spot_from_quote",
     "strategy_metrics_from_snapshot",
+    "instrument_metadata",
+    "price_per_weight_from_asset_price",
+    "weight_from_asset_quantity",
+    "asset_quantity_from_weight",
 ]