feat: Enhance currency handling and validation across scenarios

- Updated form template to prefill currency input with default value and added help text for clarity.
- Modified integration tests to assert more descriptive error messages for invalid currency codes.
- Introduced new tests for currency normalization and validation in various scenarios, including imports and exports.
- Added comprehensive tests for pricing calculations, ensuring defaults are respected and overrides function correctly.
- Implemented unit tests for pricing settings repository, ensuring CRUD operations and default settings are handled properly.
- Enhanced scenario pricing evaluation tests to validate currency handling and metadata defaults.
- Added simulation tests to ensure Monte Carlo runs are accurate and handle various distribution scenarios.

models/scenario.py

@@ -14,10 +14,11 @@ from sqlalchemy import (
     String,
     Text,
 )
-from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.orm import Mapped, mapped_column, relationship, validates
 from sqlalchemy.sql import func
 
 from config.database import Base
+from services.currency import normalise_currency
 from .metadata import ResourceType
 
 if TYPE_CHECKING:  # pragma: no cover
@@ -50,7 +51,8 @@ class Scenario(Base):
     )
     start_date: Mapped[date | None] = mapped_column(Date, nullable=True)
     end_date: Mapped[date | None] = mapped_column(Date, nullable=True)
-    discount_rate: Mapped[float | None] = mapped_column(Numeric(5, 2), nullable=True)
+    discount_rate: Mapped[float | None] = mapped_column(
+        Numeric(5, 2), nullable=True)
     currency: Mapped[str | None] = mapped_column(String(3), nullable=True)
     primary_resource: Mapped[ResourceType | None] = mapped_column(
         SQLEnum(ResourceType), nullable=True
@@ -62,7 +64,8 @@ class Scenario(Base):
         DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
     )
 
-    project: Mapped["Project"] = relationship("Project", back_populates="scenarios")
+    project: Mapped["Project"] = relationship(
+        "Project", back_populates="scenarios")
     financial_inputs: Mapped[List["FinancialInput"]] = relationship(
         "FinancialInput",
         back_populates="scenario",
@@ -76,5 +79,10 @@ class Scenario(Base):
         passive_deletes=True,
     )
 
+    @validates("currency")
+    def _normalise_currency(self, key: str, value: str | None) -> str | None:
+        # Normalise to uppercase ISO-4217; raises when the code is malformed.
+        return normalise_currency(value)
+
     def __repr__(self) -> str:  # pragma: no cover
         return f"Scenario(id={self.id!r}, name={self.name!r}, project_id={self.project_id!r})"