feat: replace nftables flush ruleset with targeted table deletion in gateway entrypoint

Remove global "flush ruleset" command from nftables configuration and add explicit "nft delete table inet nexavpn" before loading rules to avoid clearing unrelated firewall rules while ensuring clean nexavpn table state.

deploy/scripts/gateway-entrypoint.sh

@@ -104,7 +104,6 @@ EOF
   cp "${WG_GENERATED}" "${WG_CONF}"
 
   {
-    echo "flush ruleset"
     echo "table inet nexavpn {"
     echo "  chain forward {"
     echo "    type filter hook forward priority 0;"
@@ -137,6 +136,7 @@ EOF
     sysctl -w net.ipv4.ip_forward=1 >/dev/null || true
   fi
 
+  nft delete table inet nexavpn >/dev/null 2>&1 || true
   nft -f "${NFT_CONF}"
 
   if ip link show "${IFACE}" >/dev/null 2>&1; then