Backend: UTC nel DB, +00:00 nelle API, ora italiana solo in presentazione (#42)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/models/api/station.py

@@ -1,5 +1,5 @@
 """Pydantic schemas for Station and StationRecipeAssignment."""
-from datetime import datetime
+from src.backend.models.api.tipi import UtcDateTime
 from typing import Optional
 
 from pydantic import BaseModel, ConfigDict, Field
@@ -29,7 +29,7 @@ class StationResponse(BaseModel):
     notes: Optional[str]
     active: bool
     created_by: int
-    created_at: datetime
+    created_at: UtcDateTime
 
 
 class StationRecipeAssignmentCreate(BaseModel):
@@ -42,7 +42,7 @@ class StationRecipeAssignmentResponse(BaseModel):
     station_id: int
     recipe_id: int
     assigned_by: int
-    assigned_at: datetime
+    assigned_at: UtcDateTime
 
 
 class RecipeSummary(BaseModel):