feat(PORTFOLIO-001): add position-level portfolio entries

app/models/__init__.py

@@ -3,6 +3,7 @@
 from .event_preset import EventPreset, EventScenarioOverrides
 from .option import Greeks, OptionContract, OptionMoneyness
 from .portfolio import LombardPortfolio
+from .position import Position, create_position
 from .strategy import HedgingStrategy, ScenarioResult, StrategyType
 from .strategy_template import EntryPolicy, RollPolicy, StrategyTemplate, TemplateLeg
 
@@ -14,10 +15,12 @@ __all__ = [
     "LombardPortfolio",
     "OptionContract",
     "OptionMoneyness",
+    "Position",
     "ScenarioResult",
     "StrategyType",
     "StrategyTemplate",
     "TemplateLeg",
     "RollPolicy",
     "EntryPolicy",
+    "create_position",
 ]