feat(stats): #10 第②层 —— 统计页按设备过滤(per-device 本地日曲线)

镜像账户级时区曲线到「按设备」:
- migration 000018 `usage_device_hourly`(每设备 UTC 小时桶,稀疏)。
- ReportUsage deviceID>0 时加 AccumulateDeviceHourly;NodeStore 接口+impl+mock。
- usage.Store.DeviceHourlyRange(JOIN devices 校验归属+解析 uuid→id);UsageCurve
  增 deviceUUID 形参:空=账户级,非空=该设备本地日曲线(分桶逻辑复用)。
- /v1/usage?device=<uuid>;客户端 account_api.usage(device)、usageProvider key 改
  记录 (days,device)、stats_page 接 statsDeviceProvider → 选设备即重取该设备曲线。
测试:per-device 曲线隔离+归属校验(A的设备不进B)、UsageCurve(deviceUUID)、
migration v18、客户端 widget(选设备→/v1/usage 带 device=)。全量 go/flutter 绿。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/internal/usage/store.go

@@ -139,6 +139,33 @@ func (s *Store) HourlyRange(ctx context.Context, userID, fromHour, toHour int64)
 	return out, rows.Err()
 }
 
+// DeviceHourlyRange returns one device's UTC hourly buckets (usage_device_hourly)
+// for hour in [fromHour, toHour], oldest first. The JOIN both resolves the
+// client-facing device UUID to its internal id and enforces ownership (user_id),
+// so a user can never read another user's device curve.
+func (s *Store) DeviceHourlyRange(ctx context.Context, userID int64, deviceUUID string, fromHour, toHour int64) ([]HourBucket, error) {
+	rows, err := s.db.QueryContext(ctx,
+		`SELECT uh.hour, uh.bytes_up, uh.bytes_down, uh.minutes_used
+		 FROM usage_device_hourly uh
+		 JOIN devices d ON d.id = uh.device_id
+		 WHERE d.user_id = ? AND d.uuid = ? AND uh.hour BETWEEN ? AND ?
+		 ORDER BY uh.hour ASC`,
+		userID, deviceUUID, fromHour, toHour)
+	if err != nil {
+		return nil, fmt.Errorf("store.DeviceHourlyRange: %w", err)
+	}
+	defer rows.Close()
+	var out []HourBucket
+	for rows.Next() {
+		var b HourBucket
+		if err := rows.Scan(&b.Hour, &b.BytesUp, &b.BytesDown, &b.MinutesUsed); err != nil {
+			return nil, fmt.Errorf("store.DeviceHourlyRange scan: %w", err)
+		}
+		out = append(out, b)
+	}
+	return out, rows.Err()
+}
+
 // DeviceUsageRow is one device's aggregated usage over a date window, joined to
 // the devices table for display metadata.  It is the per-device ("下分设备")
 // counterpart of DailyUsage's account rollup.