fix: anchor growth forecasts to real Tehran date

internal/growthreport/adapter.go

@@ -47,10 +47,13 @@ type Builder interface {
 	Build(ctx context.Context, merchantID int64, terminalID string) (Analysis, error)
 }
 
-type PostgreSQLBuilder struct{ pool *pgxpool.Pool }
+type PostgreSQLBuilder struct {
+	pool *pgxpool.Pool
+	now  func() time.Time
+}
 
 func NewPostgreSQLBuilder(pool *pgxpool.Pool) *PostgreSQLBuilder {
-	return &PostgreSQLBuilder{pool: pool}
+	return &PostgreSQLBuilder{pool: pool, now: time.Now}
 }
 
 func (b *PostgreSQLBuilder) Build(ctx context.Context, merchantID int64, terminalID string) (Analysis, error) {
@@ -88,7 +91,7 @@ func (b *PostgreSQLBuilder) Build(ctx context.Context, merchantID int64, termina
 	if err := b.pool.QueryRow(ctx, `SELECT max(created_at AT TIME ZONE 'Asia/Tehran')::date FROM payment_sessions`).Scan(&latest); err != nil {
 		return Analysis{}, fmt.Errorf("loading dataset watermark date: %w", err)
 	}
-	forecastStart := latest.AddDate(0, 0, 1)
+	forecastStart := tehranToday(b.now())
 	peer, err := b.loadPeer(ctx, merchantID, terminalID)
 	if err != nil {
 		return Analysis{}, err