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.

schemas/imports.py

@@ -7,6 +7,7 @@ from typing import Literal
 from pydantic import BaseModel, ConfigDict, Field, field_validator, model_validator
 
 from models import MiningOperationType, ResourceType, ScenarioStatus
+from services.currency import CurrencyValidationError, normalise_currency
 
 PreviewStateLiteral = Literal["new", "update", "skip", "error"]
 
@@ -142,14 +143,13 @@ class ScenarioImportRow(BaseModel):
     @field_validator("currency", mode="before")
     @classmethod
     def normalise_currency(cls, value: Any | None) -> str | None:
-        if value is None:
+        text = _strip_or_none(value)
+        if text is None:
             return None
-        text = _normalise_string(value).upper()
-        if not text:
-            return None
-        if len(text) != 3:
-            raise ValueError("Currency code must be a 3-letter ISO value")
-        return text
+        try:
+            return normalise_currency(text)
+        except CurrencyValidationError as exc:
+            raise ValueError(str(exc)) from exc
 
     @field_validator("discount_rate", mode="before")
     @classmethod