refactor(server/db): 多库(2/4)— 时间等 DB 端计算退回 Go(可移植)

auth/admin/httpapi:把 UTC_TIMESTAMP(6) 等 DB 端取值改为 Go time.Now().UTC()
作为 ? 参数传入(两库精度一致、可测、天然跨方言)。仅这三个文件不涉及
upsert/锁,故独立成提交;其余域文件的同类改动与 dialect 改动同语句交错,合入(3/4)。

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

server/internal/httpapi/account.go

@@ -77,10 +77,10 @@ func (a *AccountAPI) GetMe(w http.ResponseWriter, r *http.Request) {
 		SELECT p.code, p.max_devices, p.daily_minutes, s.expires_at
 		FROM subscriptions s
 		JOIN plans p ON p.id = s.plan_id
-		WHERE s.user_id = ? AND s.expires_at > UTC_TIMESTAMP()
+		WHERE s.user_id = ? AND s.expires_at > ?
 		ORDER BY s.expires_at DESC
 		LIMIT 1
-	`, uid).Scan(&planCode, &maxDevices, &dailyMinutes, &expiresAt)
+	`, uid, time.Now().UTC()).Scan(&planCode, &maxDevices, &dailyMinutes, &expiresAt)
 	if err == sql.ErrNoRows {
 		planCode = "free"
 		if err := a.db.QueryRowContext(ctx,