fix(usage): 统计按客户端本地日聚合 —— 修「29号却显示28号数据」时区 bug

根因:服务端用量全按 UTC 预切天,UTC+8 用户在中国 0-8 点时 UTC 还是前一天,
「今天」就显示前一天数据。

改法(用户拍板:小时桶+查询带时区偏移):
- migration 000017 `usage_hourly`(UTC 纪元小时整数桶,稀疏存储,空小时不落行)。
- ReportUsage 同时累加 usage_hourly(按 windowEnd 的 UTC 小时);usage_daily 保留作配额/今日。
- `UsageCurve(days, offsetMin)`:读 UTC 小时桶,按客户端时区偏移**重新聚合成本地日**曲线。
- `/v1/usage?tz_offset=分钟`;客户端 `usage()` 带 `DateTime.now().timeZoneOffset.inMinutes`。
- 客户端早已「取曲线最后一点当今日」,故只改服务端聚合 + 带偏移即可。

测试:store 时区分桶证明（UTC 18:00 在 UTC vs UTC+8 落不同本地日,锁住 bug 修复）+
migration v17 + usage_hourly 表;集成测试改喂 hourly;全量 go/flutter test 绿。

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

server/internal/nodes/store.go

@@ -94,6 +94,11 @@ type NodeStore interface {
 	AccumulateUsage(ctx context.Context, userID int64, date time.Time,
 		bytesUp, bytesDown int64, minutes int64) error
 
+	// AccumulateHourly adds bytes/minutes to usage_hourly keyed by the UTC epoch
+	// hour of `hour` (for timezone-aware local-day bucketing at query time).
+	AccumulateHourly(ctx context.Context, userID int64, hour time.Time,
+		bytesUp, bytesDown int64, minutes int64) error
+
 	// AccountDayBytes returns the account's total bytes (up+down) for userID on
 	// date — the basis for the GB 综合配额 connect gate. 0 when no usage yet.
 	AccountDayBytes(ctx context.Context, userID int64, date time.Time) (int64, error)
@@ -475,3 +480,24 @@ func (s *SQLNodeStore) AccumulateUsage(
 	}
 	return nil
 }
+
+// AccumulateHourly adds bytes/minutes to usage_hourly for (userID, UTC epoch
+// hour). Epoch hour = floor(unix_seconds / 3600); the read side re-buckets these
+// into the client's local days. Idempotent within an hour.
+func (s *SQLNodeStore) AccumulateHourly(
+	ctx context.Context, userID int64, hour time.Time,
+	bytesUp, bytesDown int64, minutes int64,
+) error {
+	h := hour.UTC().Unix() / 3600
+	q := `
+		INSERT INTO usage_hourly (user_id, hour, bytes_up, bytes_down, minutes_used)
+		VALUES (?, ?, ?, ?, ?)
+		` + s.dialect.Upsert([]string{"user_id", "hour"},
+		"bytes_up = bytes_up + EXCLUDED.bytes_up",
+		"bytes_down = bytes_down + EXCLUDED.bytes_down",
+		"minutes_used = minutes_used + EXCLUDED.minutes_used")
+	if _, err := s.db.ExecContext(ctx, q, userID, h, bytesUp, bytesDown, minutes); err != nil {
+		return fmt.Errorf("nodes.SQLNodeStore.AccumulateHourly: %w", err)
+	}
+	return nil
+}