fix(cli): honor configured gateway port

[MicroMilo]

Summary

• use gateway.port from the loaded config snapshot when no CLI --port or PILOTDECK_GATEWAY_PORT is provided
• preserve existing precedence: CLI flag, environment variable, config, default 18789

Verification

• npm exec -- tsc --noEmit -p tsconfig.json

Notes

This is a real config/runtime mismatch: gateway.port was parsed into the config snapshot but the server startup path ignored it.

[MicroMilo]

Validation note:

This PR fixes a real config/runtime mismatch.

gateway.port is already part of the parsed config snapshot, but the previous server startup path did not consume it. Startup only respected the CLI port, PILOTDECK_GATEWAY_PORT, or the hardcoded default 18789. Therefore, a configured gateway.port value was accepted by config parsing but ignored by the actual gateway startup path.

This PR updates the startup precedence to:

CLI --port > PILOTDECK_GATEWAY_PORT > gateway.port > 18789

Validation command currently listed by this PR:

npm exec -- tsc --noEmit -p tsconfig.json

The behavior change is clear, but the validation should be strengthened. A small unit test around port resolution would make this PR much easier to review. It should cover:

• CLI port wins over all other sources;
• environment port wins over config;
• gateway.port is used when CLI/env are absent;
• 18789 is used when no source provides a port.

This would turn the precedence rule into executable self-validation.