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/store/sqlite_migrate_test.go

@@ -29,8 +29,8 @@ func TestSQLiteMigrateUpDown(t *testing.T) {
 	if dirty {
 		t.Fatalf("schema dirty after MigrateUp")
 	}
-	if v != 16 {
-		t.Errorf("version = %d, want 16", v)
+	if v != 17 {
+		t.Errorf("version = %d, want 17", v)
 	}
 
 	// 2. Core tables exist.
@@ -38,7 +38,7 @@ func TestSQLiteMigrateUpDown(t *testing.T) {
 		"users", "devices", "plans", "subscriptions", "code_batches", "codes",
 		"usage_daily", "audit_log", "providers", "nodes", "node_events",
 		"directory_version", "provision_idempotency", "replacements", "admins",
-		"connect_credentials", "usage_device_daily", "sessions",
+		"connect_credentials", "usage_device_daily", "sessions", "usage_hourly",
 	} {
 		var name string
 		err := db.QueryRow(

server/internal/store/usage_tz_test.go

@@ -0,0 +1,64 @@
+package store_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/wangjia/pangolin/server/internal/usage"
+)
+
+// The timezone-fix proof: usage stored at UTC 18:00 yesterday must land on a
+// DIFFERENT local calendar day under UTC (offset 0) vs UTC+8 (offset 480) —
+// exactly the "今天却显示昨天数据" bug. UsageCurve re-buckets UTC hourly rows by
+// the client's local day so "today" matches the user's calendar.
+func TestSQLite_UsageCurve_LocalDayBucketing(t *testing.T) {
+	ctx := context.Background()
+	db := openSQLite(t)
+
+	// Yesterday 18:00 UTC = today 02:00 in UTC+8 → straddles the day boundary.
+	now := time.Now().UTC()
+	y := now.AddDate(0, 0, -1)
+	utc18 := time.Date(y.Year(), y.Month(), y.Day(), 18, 0, 0, 0, time.UTC)
+	hourEpoch := utc18.Unix() / 3600
+	if _, err := db.Exec(
+		`INSERT INTO usage_hourly (user_id, hour, bytes_up, bytes_down, minutes_used) VALUES (1,?,?,?,?)`,
+		hourEpoch, 1000, 2000, 5); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+
+	cn := time.FixedZone("UTC+8", 8*3600)
+	utcDate := utc18.Format("2006-01-02")    // yesterday (UTC)
+	cnDate := utc18.In(cn).Format("2006-01-02") // today (UTC+8)
+	if utcDate == cnDate {
+		t.Fatalf("test setup expected different dates, got %s == %s", utcDate, cnDate)
+	}
+
+	svc := usage.NewService(usage.NewStore(db), nil, nil, time.Hour)
+
+	find := func(days, offset int, date string) (usage.UsagePoint, bool) {
+		pts, e := svc.UsageCurve(ctx, 1, days, offset)
+		if e != nil {
+			t.Fatalf("UsageCurve(off=%d): %v", offset, e)
+		}
+		for _, p := range pts {
+			if p.Date == date {
+				return p, true
+			}
+		}
+		return usage.UsagePoint{}, false
+	}
+
+	// Offset 0 (UTC): the data is on yesterday's UTC date.
+	if p, ok := find(3, 0, utcDate); !ok || p.BytesDown != 2000 || p.BytesUp != 1000 || p.MinutesUsed != 5 {
+		t.Fatalf("UTC bucket: want data on %s, got ok=%v %+v", utcDate, ok, p)
+	}
+	// Offset +480 (UTC+8): the SAME data is on today's local date instead.
+	if p, ok := find(3, 480, cnDate); !ok || p.BytesDown != 2000 {
+		t.Fatalf("UTC+8 bucket: want data on %s, got ok=%v %+v", cnDate, ok, p)
+	}
+	// And under +480 it must NOT appear on the UTC date.
+	if p, ok := find(3, 480, utcDate); ok && p.BytesDown != 0 {
+		t.Fatalf("UTC+8: data leaked onto UTC date %s: %+v", utcDate, p)
+	}
+}