Standardize deployment env and deployer handling

scripts/deployment/configure-avalanche-arbitrum-cronos-bridges.sh

@@ -59,7 +59,6 @@ _gas138="--legacy --gas-limit 250000 --gas-price 2000000000"
 _gas_remote="--legacy --gas-limit 400000"
 
 PRIVATE_KEY="${PRIVATE_KEY:-}"
-[[ -n "$PRIVATE_KEY" && ! "$PRIVATE_KEY" =~ ^0x ]] && PRIVATE_KEY="0x$PRIVATE_KEY"
 
 DRY_RUN="${DRY_RUN:-0}"
 RED='\033[0;31m'
@@ -86,8 +85,7 @@ run_or_echo() {
 echo -e "${GREEN}=== Avalanche/Arbitrum/Cronos ↔ Chain 138 Bridge Configuration ===${NC}"
 echo ""
 
-if [[ -z "$PRIVATE_KEY" ]]; then
-  echo -e "${RED}ERROR: PRIVATE_KEY not set${NC}"
+if ! require_private_key_env; then
   exit 1
 fi