Enable payload-validation for Linea Maru

Set payload-validation-enabled=true in Maru config to ensure
payloads are sent to the execution client. Without this, Maru
doesn't send forkchoice/newPayload calls when EL reports synced
status (even at block 0).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

linea/mainnet/maru/config.toml.template

@@ -31,7 +31,7 @@ refresh-interval = "3s"
 # Besu and Geth node as execution layer client
 engine-api-endpoint = { endpoint = "http://${EL_HOST}:8551", jwt-secret-path = "/jwtsecret" }
 eth-api-endpoint = { endpoint = "http://${EL_HOST}:8545" }
-payload-validation-enabled = false
+payload-validation-enabled = true
 
 [observability]
 port = 9090