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/recipe.py

@@ -1,5 +1,5 @@
 """Pydantic schemas for Recipe and RecipeVersion operations."""
-from datetime import datetime
+from src.backend.models.api.tipi import UtcDateTime
 from typing import Optional, TYPE_CHECKING
 
 from pydantic import BaseModel, ConfigDict, Field
@@ -51,7 +51,7 @@ class RecipeVersionResponse(BaseModel):
     version_number: int
     is_current: bool
     created_by: int
-    created_at: datetime
+    created_at: UtcDateTime
     change_notes: Optional[str] = None
     tasks: list["TaskResponse"] = []
 
@@ -72,7 +72,7 @@ class RecipeResponse(BaseModel):
     requires_serial: bool = False
     allow_manual_input: bool = False
     created_by: int
-    created_at: datetime
+    created_at: UtcDateTime
     active: bool
     current_version: Optional[RecipeVersionResponse] = None