feat: Add Processing Opex functionality

- Introduced OpexValidationError for handling validation errors in processing opex calculations.
- Implemented ProjectProcessingOpexRepository and ScenarioProcessingOpexRepository for managing project and scenario-level processing opex snapshots.
- Enhanced UnitOfWork to include repositories for processing opex.
- Updated sidebar navigation and scenario detail templates to include links to the new Processing Opex Planner.
- Created a new template for the Processing Opex Planner with form handling for input components and parameters.
- Developed integration tests for processing opex calculations, covering HTML and JSON flows, including validation for currency mismatches and unsupported frequencies.
- Added unit tests for the calculation logic, ensuring correct handling of various scenarios and edge cases.

models/project.py

@@ -6,6 +6,7 @@ from typing import TYPE_CHECKING, List
 from .enums import MiningOperationType, sql_enum
 from .profitability_snapshot import ProjectProfitability
 from .capex_snapshot import ProjectCapexSnapshot
+from .processing_opex_snapshot import ProjectProcessingOpexSnapshot
 
 from sqlalchemy import DateTime, ForeignKey, Integer, String, Text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
@@ -67,6 +68,13 @@ class Project(Base):
         order_by=lambda: ProjectCapexSnapshot.calculated_at.desc(),
         passive_deletes=True,
     )
+    processing_opex_snapshots: Mapped[List["ProjectProcessingOpexSnapshot"]] = relationship(
+        "ProjectProcessingOpexSnapshot",
+        back_populates="project",
+        cascade="all, delete-orphan",
+        order_by=lambda: ProjectProcessingOpexSnapshot.calculated_at.desc(),
+        passive_deletes=True,
+    )
 
     @property
     def latest_profitability(self) -> "ProjectProfitability | None":
@@ -84,5 +92,13 @@ class Project(Base):
             return None
         return self.capex_snapshots[0]
 
+    @property
+    def latest_processing_opex(self) -> "ProjectProcessingOpexSnapshot | None":
+        """Return the most recent processing opex snapshot, if any."""
+
+        if not self.processing_opex_snapshots:
+            return None
+        return self.processing_opex_snapshots[0]
+
     def __repr__(self) -> str:  # pragma: no cover - helpful for debugging
         return f"Project(id={self.id!r}, name={self.name!r})"