fix: sync sadhna calendar with local timezone

internal/repository/sadhna_repo.go

@@ -15,6 +15,20 @@ type SadhnaRepo struct{ pg *Postgres }
 
 func NewSadhnaRepo(pg *Postgres) *SadhnaRepo { return &SadhnaRepo{pg: pg} }
 
+// UserTimezone returns the user's stored IANA timezone, or "" if unset — the
+// caller falls back to a default. Kept here so the sādhana day boundary can
+// be the user's local midnight.
+func (r *SadhnaRepo) UserTimezone(ctx context.Context, userID string) (string, error) {
+	var tz string
+	err := r.pg.Pool.QueryRow(ctx,
+		`SELECT COALESCE(NULLIF(timezone, ''), '') FROM users WHERE id = $1`, userID,
+	).Scan(&tz)
+	if err != nil {
+		return "", err
+	}
+	return tz, nil
+}
+
 // UpsertToday records (or updates) the given day's chanting progress for
 // the user. The caller passes the UTC calendar date explicitly (rather
 // than relying on the DB's CURRENT_DATE) so day bucketing stays identical