fix(backtest): remove BT-001A exact window restriction now that full data access is available

- Change WindowPolicy from EXACT to BOUNDED for backtest fixture
- Pass data_source to run_read_only_scenario so real data can be used
- Fix injected provider identity preservation in BacktestPageService
- Add type: ignore for BacktestHistoricalProvider protocol assignment
- Revert TypedDict change to avoid cascading type issues in pages/
- Update tests to reflect new BOUNDED policy behavior

app/domain/portfolio_math.py

@@ -268,7 +268,7 @@ def portfolio_snapshot_from_config(
     config: PortfolioConfig | None = None,
     *,
     runtime_spot_price: float | None = None,
-) -> PortfolioSnapshot:
+) -> dict[str, float | str]:
     """Build portfolio snapshot with display-mode-aware calculations.
 
     In GLD mode:
@@ -392,7 +392,7 @@ def build_alert_context(
 
 
 def strategy_metrics_from_snapshot(
-    strategy: dict[str, Any], scenario_pct: int, snapshot: PortfolioSnapshot
+    strategy: dict[str, Any], scenario_pct: int, snapshot: dict[str, Any]
 ) -> dict[str, Any]:
     spot = decimal_from_float(float(snapshot["spot_price"]))
     gold_weight = _gold_weight(float(snapshot["gold_units"]))