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/api/routers/setup.py

@@ -6,6 +6,7 @@ NOT protected by API Key auth (standalone access).
 import hmac
 import random
 from datetime import datetime, timedelta
+from src.backend.utils.tempo import utcnow
 from pathlib import Path
 
 from alembic import command
@@ -555,7 +556,7 @@ async def seed_demo_data(body: PasswordBody):
             tec_user = created_users[2]  # tec1
             lot_numbers = ["LOT-2025-001", "LOT-2025-002", "LOT-2025-003", "LOT-2025-004"]
             serial_numbers = [f"SN-{i:04d}" for i in range(1, 13)]
-            base_date = datetime.now()
+            base_date = utcnow()
 
             all_subtasks = subtasks_1 + subtasks_2
             measurements_created = 0