chore(config): clarify catchup_lag_threshold=1 rejection message

Reword the ValidateBasic error for catchup_lag_threshold == 1 from
"to absorb round skew" to "(margin beyond the one-height round skew)".
Rejecting 1 isn't required to absorb a one-height skew; the point is to
keep the smallest enabled threshold above the routine one-height
proposer/commit difference between synced peers. Message text only; no
logic change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: pratikspatil024

config/config.go

@@ -1181,7 +1181,7 @@ func (cfg *ConsensusConfig) ValidateBasic() error {
 		return errors.New("catchup_lag_threshold can't be negative")
 	}
 	if cfg.CatchupLagThreshold == 1 {
-		return errors.New("catchup_lag_threshold must be 0 (disabled) or >=2 to absorb round skew")
+		return errors.New("catchup_lag_threshold must be 0 (disabled) or >=2 (margin beyond the one-height round skew)")
 	}
 	if cfg.CatchupDebounceDuration < 0 {
 		return errors.New("catchup_debounce_duration can't be negative")