fix: respect gateway port from config file

[jasonQin6]

Problem

The nanobot gateway command ignores the gateway.port setting from the config file (~/.nanobot/config.json). The CLI --port option has a hardcoded default value of 18790, which always takes precedence over the config file setting.

Root Cause

In nanobot/cli/commands.py, the gateway function:

1. Uses typer.Option(18790, ...) as the default port value
2. Never reads config.gateway.port from the loaded configuration

Solution

1. Changed --port option default to None instead of 18790
2. Load config first, then use port or config.gateway.port to get the actual port
3. This allows config file to set the default, while CLI --port can still override it

Testing

# With config.gateway.port = 18880 in ~/.nanobot/config.json
nanobot gateway  # Should use port 18880 from config
nanobot gateway --port 19999  # Should use port 19999 from CLI

Related

• Config schema already defines GatewayConfig.port with default 18790 in nanobot/config/schema.py