feat: Implement initial capex calculation feature

- Added CapexComponentInput, CapexParameters, CapexCalculationRequest, CapexCalculationResult, and related schemas for capex calculations.
- Introduced calculate_initial_capex function to aggregate capex components and compute totals and timelines.
- Created ProjectCapexRepository and ScenarioCapexRepository for managing capex snapshots in the database.
- Developed capex.html template for capturing and displaying initial capex data.
- Registered common Jinja2 filters for formatting currency and percentages.
- Implemented unit and integration tests for capex calculation functionality.
- Updated unit of work to include new repositories for capex management.

services/exceptions.py

@@ -37,3 +37,14 @@ class ProfitabilityValidationError(Exception):
 
     def __str__(self) -> str:  # pragma: no cover - mirrors message for logging
         return self.message
+
+
+@dataclass(eq=False)
+class CapexValidationError(Exception):
+    """Raised when capex calculation inputs fail domain validation."""
+
+    message: str
+    field_errors: Sequence[str] | None = None
+
+    def __str__(self) -> str:  # pragma: no cover - mirrors message for logging
+        return self.message