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_scenario_pricing.py

@@ -0,0 +1,120 @@
+from __future__ import annotations
+
+import pytest
+
+from models import MiningOperationType, Project, Scenario, ScenarioStatus
+from services.pricing import PricingInput, PricingMetadata
+from services.scenario_evaluation import ScenarioPricingConfig, ScenarioPricingEvaluator
+
+
+def build_scenario() -> Scenario:
+    project = Project(name="Test Project",
+                      operation_type=MiningOperationType.OPEN_PIT)
+    scenario = Scenario(
+        project=project,
+        project_id=1,
+        name="Scenario A",
+        status=ScenarioStatus.ACTIVE,
+        currency="USD",
+    )
+    scenario.id = 1  # simulate persisted entity
+    return scenario
+
+
+def test_scenario_pricing_evaluator_uses_metadata_defaults() -> None:
+    scenario = build_scenario()
+    evaluator = ScenarioPricingEvaluator(
+        ScenarioPricingConfig(
+            metadata=PricingMetadata(
+                default_currency="USD", default_payable_pct=95)
+        )
+    )
+    inputs = [
+        PricingInput(
+            metal="copper",
+            ore_tonnage=50_000,
+            head_grade_pct=1.0,
+            recovery_pct=90,
+            payable_pct=None,
+            reference_price=9_000,
+            treatment_charge=50_000,
+            smelting_charge=10_000,
+            moisture_pct=9,
+            moisture_threshold_pct=None,
+            moisture_penalty_per_pct=None,
+            impurity_ppm={"As": 120},
+            premiums=10_000,
+            fx_rate=1.0,
+            currency_code=None,
+        )
+    ]
+
+    snapshot = evaluator.evaluate(scenario, inputs=inputs)
+
+    assert snapshot.scenario_id == scenario.id
+    assert len(snapshot.results) == 1
+    result = snapshot.results[0]
+    assert result.currency == "USD"
+    assert result.net_revenue > 0
+
+
+def test_scenario_pricing_evaluator_override_metadata() -> None:
+    scenario = build_scenario()
+    evaluator = ScenarioPricingEvaluator(ScenarioPricingConfig())
+    metadata_override = PricingMetadata(
+        default_currency="CAD",
+        default_payable_pct=90,
+        moisture_threshold_pct=5,
+        moisture_penalty_per_pct=500,
+    )
+
+    inputs = [
+        PricingInput(
+            metal="copper",
+            ore_tonnage=20_000,
+            head_grade_pct=1.2,
+            recovery_pct=88,
+            payable_pct=None,
+            reference_price=8_200,
+            treatment_charge=15_000,
+            smelting_charge=6_000,
+            moisture_pct=6,
+            moisture_threshold_pct=None,
+            moisture_penalty_per_pct=None,
+            premiums=5_000,
+            fx_rate=1.0,
+            currency_code="cad",
+        ),
+        PricingInput(
+            metal="gold",
+            ore_tonnage=5_000,
+            head_grade_pct=2.0,
+            recovery_pct=90,
+            payable_pct=None,
+            reference_price=60_000,
+            treatment_charge=10_000,
+            smelting_charge=5_000,
+            moisture_pct=4,
+            moisture_threshold_pct=None,
+            moisture_penalty_per_pct=None,
+            premiums=15_000,
+            fx_rate=1.0,
+            currency_code="cad",
+        ),
+    ]
+
+    snapshot = evaluator.evaluate(
+        scenario,
+        inputs=inputs,
+        metadata_override=metadata_override,
+    )
+
+    assert len(snapshot.results) == 2
+    assert all(result.currency ==
+               scenario.currency for result in snapshot.results)
+
+    copper_result = snapshot.results[0]
+    expected_payable = 20_000 * 0.012 * 0.88 * 0.90
+    assert copper_result.payable_metal_tonnes == pytest.approx(
+        expected_payable)
+    assert sum(result.net_revenue for result in snapshot.results) > 0