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/statistics.py

@@ -1,5 +1,5 @@
 """Pydantic schemas for SPC statistics responses."""
-from datetime import datetime
+from src.backend.models.api.tipi import UtcDateTime, UtcNaiveInput
 from typing import Optional
 
 from pydantic import BaseModel, Field
@@ -10,8 +10,8 @@ class StatisticsQuery(BaseModel):
     recipe_id: int
     version_id: Optional[int] = None
     subtask_id: Optional[int] = None
-    date_from: Optional[datetime] = None
-    date_to: Optional[datetime] = None
+    date_from: UtcNaiveInput = None
+    date_to: UtcNaiveInput = None
     operator_id: Optional[int] = None
     lot_number: Optional[str] = None
     serial_number: Optional[str] = None
@@ -20,7 +20,7 @@ class StatisticsQuery(BaseModel):
 class ControlChartData(BaseModel):
     """Data for X-bar/R control chart."""
     values: list[float]
-    timestamps: list[datetime]
+    timestamps: list[UtcDateTime]
     mean: float
     ucl: float  # Upper Control Limit
     lcl: float  # Lower Control Limit
@@ -60,7 +60,7 @@ class CapabilityData(BaseModel):
 
 class TrendData(BaseModel):
     """Temporal trend data for capability indices."""
-    dates: list[datetime]
+    dates: list[UtcDateTime]
     cpk_values: list[Optional[float]]
     ppk_values: list[Optional[float]]
     n_per_period: list[int]