Enhance UI rendering and add unit tests for simulation functionality

- Updated the `_render` function in `ui.py` to correctly pass the request object to `TemplateResponse`.
- Initialized `upcoming_maintenance` as a typed list in `_load_dashboard` for better type safety.
- Added new unit tests in `test_simulation.py` to cover triangular sampling and uniform distribution defaults.
- Implemented a test to ensure that running the simulation without parameters returns an empty result.
- Created a parameterized test in `test_ui_routes.py` to verify that additional UI routes render the correct templates and context.

routes/ui.py

@@ -40,7 +40,8 @@ def _render(
     template_name: str,
     extra: Optional[Dict[str, Any]] = None,
 ):
-    return templates.TemplateResponse(template_name, _context(request, extra))
+    context = _context(request, extra)
+    return templates.TemplateResponse(request, template_name, context)
 
 
 def _format_currency(value: float) -> str:
@@ -436,7 +437,7 @@ def _load_dashboard(db: Session) -> Dict[str, Any]:
     recent_simulations.sort(key=lambda item: item["iterations"], reverse=True)
     recent_simulations = recent_simulations[:5]
 
-    upcoming_maintenance = []
+    upcoming_maintenance: list[Dict[str, Any]] = []
     for record in (
         db.query(Maintenance)
         .order_by(Maintenance.maintenance_date.asc())