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.

tests/test_import_parsing.py

@@ -140,3 +140,22 @@ def test_scenario_import_handles_large_dataset() -> None:
 
     assert len(result.rows) == 500
     assert len(result.rows) == 500
+
+
+def test_scenario_import_rejects_invalid_currency() -> None:
+    csv_content = dedent(
+        """
+        project_name,name,currency
+        Project A,Scenario Invalid,US
+        """
+    ).strip()
+    stream = BytesIO(csv_content.encode("utf-8"))
+
+    result = load_scenario_imports(stream, "scenarios.csv")
+
+    assert not result.rows
+    assert result.errors
+    error = result.errors[0]
+    assert error.row_number == 2
+    assert error.field == "currency"
+    assert "Invalid currency code" in error.message