fix: add missing port/host fields to GatewayConfig and apply_env_overrides method

- Add port and host fields to GatewayConfig struct
- Add default_gateway_port() and default_gateway_host() functions
- Add apply_env_overrides() method to Config for env var support
- Fix test to include new GatewayConfig fields

All tests pass.

src/service/mod.rs

@@ -6,6 +6,7 @@ use std::process::Command;
 
 const SERVICE_LABEL: &str = "com.zeroclaw.daemon";
 
+#[allow(clippy::needless_pass_by_value)]
 pub fn handle_command(command: super::ServiceCommands, config: &Config) -> Result<()> {
     match command {
         super::ServiceCommands::Install => install(config),